No, he's just being brutally honest because of limited time. They will understand that. It demonstrates their enemy is capable and intelligent. People cutting him off just proves their handlers don't want them to have this important info and the Ukrainians don't mean them harm if they just don't join the russian army. They might ponder the thought the Ukrainian is exaggerating, but there wasn't much to exaggerate in the message. He didn't boast about strength or numbers. Just simple facts.

Defending your home/country from an invading enemy is not being an asshole.

Well... good luck to you. I wish you godspeed in your quest to put one over on the asshole who warned you against invading his homeland. Hope you're quick enough to dodge the first couple dozen drones he sends your way.

Edit: In case it's not clear, I'm explicitly hoping that you, personally, die in a fire.

Around how many corners do you have to think so that makes sense?

They are probably already taught that

strongly disagree with this message making an ukrainian soldier an asshole but I will say this is maybe effective propaganda for those who are pro-Ukrainian but not so effective in speaking to a russian audience. I imagine what could have worked better for them for example would have been for him to speak at length about the horrors of war and question the point of it all from the Russian invading soldier's POV before revealing himself as Ukrainian.