Making a lot of assumptions and claims about a literal fantasy creature.

The specific details aren’t important, but yeah. A lot less HP than can survive 10d10 damage.

They’re introducing the BBEG to a level 1 party, so that barbarian probably only has around 10 hp

I play using a VTT so everybody sees what the results are immediately. No telling it to them gently when the troll crits three times during the fight.