Again, Armenian is not totally a Satem language and the Satemization is based on only a small numbers of words. Remember too, Armenian rests between Indo-Iranian and Greek languages, so it would make sense that it's a mostly-but-not-quite Satem language. Balto-Slavic languages (including Latvian) are also Satem but also still have some Centemized words, which some have suggested means that Satemization wasn't complete in Balto-Slavic languages, for whatever reason. So perhaps Armenian features a similar phenomenon, a Satemization process that was incomplete or interrupted for whatever reason.
As for my comment about IE migration into Armenia, I meant specifically the people that introduced the (proto) Armenian language. Theoretically, they would have been a Steppe-derived population, but, to my understanding, they left almost no traces of Steppe-derived ancestry in modern Armenians. In other words, modern Armenians are more similar to the EBA, pre-IE/non-Steppe people of the region. So if there were Steppe Armenians (i.e. a Yamnaya-derived population who brought the proto-Armenian language to Armenia), where did they go? They were either a) an extremely small number of people/elite class who didn't really mix in at all with the native population, which is certainly possible, and then died off or b) they didn't die off, but migrated elsewhere from Armenia. But if they migrated elsewhere, regardless of sound changes, if we can recognize that Greek and Indo-Iranian languages are closest to Armenian, and theoretically these branches split off from one another before proto-Armenian was fully developed (and proto-Greek and proto-Indo Iranian) we should be able to identify another Armenian language that derives from the Steppe Armenians and is closer to Armenian than Greek or Indo-Iranian. Meaning, a sister language to Armenian (AKA another daughter of the proto-Armenian). But obviously there is no evidence of this, so it suggests that the Steppe Armenians died off. Unless it was Phrygian (which is now thought to be closer to Greek than Armenian, so it might not be a good candidate) or some unattested language.