PokerStars No-Limit Hold'em, $0.50 BB (9 handed) Poker-Stars Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

UTG ($45.35)
UTG+1 ($82.50)
MP1 ($26.95)
MP2 ($27.80)
MP3 ($48)
CO ($62.15)
Hero ($50)
SB ($53.65)
BB ($68.95)

Preflop: Hero is Button with K, A.
UTG calls $0.50, 1 fold, MP1 calls $0.50, 3 folds, Hero raises to $3, 2 folds, UTG calls $2.50, MP1 folds.

Flop: ($7.25) K, J, 6 (2 players)
UTG checks, Hero checks.

Turn: ($7.25) A (2 players)
UTG bets $5, Hero calls $5.

River: ($17.25) 3 (2 players)
UTG bets $7.5, Hero calls $7.50.

Final Pot: $32.25

UTG was a passive nit, like 20/4 over a small sample, but hugely nitty postflop. I saw him flop flush and check it down til the river. The main reason I decided to play it like this was because he insta called preflop, then proceeded to time bank 30 seconds before checking the flop. There is no way he is multi-tabling so he didn't just time out. Should I still bet this flizzop?

edit - turn and river bets insta