Those people were not soldiers, but gladiators - here is a documentary about them (in total 80, but DNA of 6 was tested):
http://watchdocumentary.org/watch/gladiators-back-from-the-dead-video_13d4008d0.html
Angela is right that millet wasn't totally unknown to the Romans, also user Vettor from Anthrogenica noticed this - quote:
(however, this refers to Republican times, several centuries before the lifetime of those gladiators from York):
So unless those gladiators were 300 years old (and they were less than 45 years old), they did not spend childhood in BC times.
Moreover - the fact remains, that in PCA (Figure 1.) one of gladiators clusters autosomally firmly within E.Europe (Ru - Russia?):
http://www.nature.com/ncomms/2016/160119/ncomms10326/fig_tab/ncomms10326_F1.html
And in IBS (Figure 2.) the combined sample of gladiators (excluding Near Easterner) shows similarities to Lithuanians and Poles:
http://www.nature.com/ncomms/2016/160119/ncomms10326/fig_tab/ncomms10326_F2.html
The following is from the description of the documentary at the site to which you linked:
"The men were also all buried with some respect and their final resting places included grave goods as well as large joints of meat – making it less likely they were executed criminals.
But the theory they were gladiators is still open to dispute. As yet there has been no evidence of an amphitheatre found in York and there is nothing conclusive about the men’s injuries.
They could have been inflicted in battle and there were no injuries from weapons like the three-pointed trident which were specifically used by certain types of gladiator.
Because of this York Archaeological Trust has set up a website offering the public the chance to have their say. Opinions can be left at at headlessromans.co.uk.
John Walker, York Archaeological Trust’s chief executive, said: “This is a fascinating discovery that gives a real insight into the world of interpreting archaeology.”
“With archaeology, you are very rarely dealing in the definite. There are almost always elements of ‘possibly’ and ‘probably’ and the archaeologist’s job is to weigh up the evidence and make an informed judgment on the most likely explanation.”
Journalists sensationalize; scholars usually don't. I'll add again that the usual method of execution for gladiators was a single sword thrust from behind down through the neck, not hacking repeatedly with dull blades, which is what these remains show. Also, I find it unusual that the remains had grave goods; the run of the mill gladiator wasn't treated with this kind of respect. The puncture wounds could be post-mortem for all we know, from a bear. That would be very likely if these men were auxiliaries who were killed somewhere nearer the wall and left there before being retrieved. On the other hand, if they were auxiliaries one would think there would be some military paraphernalia buried with them, unless their bodies were stripped after their death.This discussion reminds me of the ones that surrounded the discovery of Oetzi; lots of conjecture but little proof.
I'm keeping an open mind.
As to the millet, perhaps you didn't have time to read the paper I posted, Tomenable, or look at the map of where it was grown. It wasn't grown just in Republican times, and the Romans raised a lot of it, as the ancient literature indicates. It's just that they gave it to animals and the poor. The fact that there aren't that many finds is probably due to the fact that it was usually pounded, turned into flour, and then boiled for human consumption. To eat it in bread form was unpopular because the bread was so dense and so hard on the teeth. There are pictures of what the teeth look like after a life time of eating bread made from it.
This is how it was usually eaten by humans in the Roman world.
The important fact is that the six Romano-Brits cluster with each other and with the Iron Age British sample and with the modern Welsh most of all. Now, maybe that autosomal signature also existed in France and nearby areas, and maybe there was some variation among them, with one sample having picked up some ancestry, maybe through the Belgae, that had more of an "eastern" leaning, but none of those six, who aren't even the ones who show evidence of having eaten millet, shows evidence of recent ancestry from Russia.
I mean, I understand wanting to identify with ancient people, Tomenable, and for men, perhaps with soldiers or gladiators, but it's as if you want the Slavs to be like Forest Gump, present and crucial at every stage of human history.
It doesn't work like that for any group.