Russian disinfo aside, it is admittedly seeming likely that Ukraine did fire those missiles.
President Joe Biden says it was “unlikely” that a missile that killed two in NATO-ally Poland was fired from Russia
apnews.com
Sort of. Biden said it's unlikely that the missile was fired
from Russia according to trajectory data. But of course, the Russian military could also have fired it from occupied Ukrainian territory (or even from Belarus). Plus, the Polish government-- the authorities with the easiest access to the wreckage site-- has said it was "Russian-made" (though of course that also doesn't
necessarily mean it was fired by Russia).
Analysts have said (based on wreckage photographs) that the remnants look quite similar to the S-300 munitions. Which are used by both Ukraine and Russia, frustratingly, so that doesn't help us hugely.
There's also the fact that it occurred when Russia launched over a hundred other missiles all over Ukraine, including into the West of the country. And the head of RT (which if of course state-sanctioned) gloated about it on Twitter.
But yeah. Far from certain. Could also be a Ukrainian air defence missile fired during the bombardment. Gotta wait for investigation.