It may be the US Gov purchased it for target practice.
Or captured it in some war or another. Whoops -- I missed that it was from the war in Ukraine. I guess that's "some war or another"
I have no personal experience, but I know that you want to get your hands on enemy hardware so you can see how well it actually works, what it's strong and weak spots are, and if they've done something really amazing then steal the technology.
If I were guessing, I'd guess that in return for all the intelligence we're giving
them, the Ukrainians are sharing Russian hardware with
us, so we can dissect it. How that tank ended up
there however -- huh?
I bet there's some US general who's saying "huh?" in some profanity-laced and "heads will roll once we find out who" sort of way.
At least for a while, the Allied forces in Europe flow their high-altitude missions using oxygen bottles captured from German airplanes, because the Germans just made better ones.