Saw this hand in the Pokerstars replayer at 200NL and it didn't make sense to me.

200NL Zoom Pokerstars, $441 effective stacks

HJ (EluSiveMark) opens $5.18
BTN (danielkyosev) 3bets to $20
HJ 4bets to $61
BTN calls

Flop ($125) Kc Jd 7h
HJ checks
BTN checks

Turn ($125) Kc Jd 7h [Qd}
HJ checks
BTN bets $52
HJ calls

River ($229) Kc Jd 7h Qd [As]
HJ bets $209
BTN raises to $329
HJ calls

BTN shows T7s and wins with a straight
HJ shows AA

Obviously the preflop play from BTN is terrible, but I don't understand the river donk bet/call from EluSiveMark. Is the idea here that he has more Tx/AA/KK based on preflop play so he wants to donk on the rivered Ace? Also why does he choose this sizing of 90% pot leaving so little behind? Would EluSiveMark's bluffs be 98s/2p hands here on the river?