Very confused with paternal haplogroup I-BY51204

So this is most likely a great grandfather of mine's paternal haplogroup. This belongs to Z-58, which seems to be western germanic. If it helps, his last name was Tate, from Illinois. His family came from northern Ireland, but originally from Lincolnshire England. I have heard of viking origins of the family name, but I am not sure if that's true. On scaled innovation, SNP tracker, it states that it arrived in England during the viking age (around 900), and arrived at a place where raids/settlement commonly occurred (N. Yorkshire). The SNP tracker website also displays a map, showing that it originated in Eastern denmark, and went to North eastern England. So my question is, why is this a western germanic haplogroup, but arrives in England during the viking age, and at a place where vikings went? If this isn't norse, what is it doing there so late after the Anglo-Saxon migration?

Yes it is confusing because researchers in this area have segmented a split of Norse from North sea /West Germanic in the Y tree. We know this oversimplifies the situation as most likely all Z140 originated in modern day Denmark which has had speakers of both Norse & West germanic dialects within its kingdom's territory at the relevant times . It also gets confusing because many of the Angles and Saxons involved in the major settlement events of Britain post Roman collapse would have spoken West Germanic dialects hence Old English / Old Scots yet several hundred years later Norse speakers bearing the same Z140 clades invaded or settled as Vikings. Also a word of advice, I wouldn't take too much from these SNP trackers as the algorithms are victims of a lack of sampling data in many cases, limitations within the algorithms & a necessary bias of data towards modern testing distribution equaling ancient distribution.