Both sides release propaganda. This is war, propaganda is ammo. You can prefer one sides propaganda if it turns out their reporting of facts accords better with third party confirmation or the admissions of the other side. In this case, Polish sources contradict this story, it is false.
The Ukrainian MOD information so far is generally correct, though I doubt some of it. Specific claims tend to be backed up with plausible video. Russian MOD claims usually aren’t.
I doubt Uke MOD statistical claims of Russian losses, as in a general historical context kill claims are overstated, even if honestly intended. Everyone is an optimist on these things. Russian MOD estimates are much less trustworthy IMHO.
Ukraine refuses to release the number of Ukrainians that have been injured or killed in this pointless war. Makes the propaganda easier to swallow that way.