NL10 weird river bluff after scattered action in squeeze pot

PokerStars Zoom, Hold'em No Limit - $0.05/$0.10 - 6 players

UTG: $5.23 (52 bb)
MP: $3.03 (30 bb)
CO: $10.25 (103 bb)
BU: $19.13 (191 bb)
SB: $21.77 (218 bb)
BB (Hero): $30.43 (304 bb)

Pre-Flop: ($0.15) Hero is BB with K♠ 9♠
1 fold, MP calls $0.10, 1 fold, BTN raises to $0.30, SB calls $0.25, Hero 3-bets to $1.30, MP calls $1.20, 1 fold, SB calls $1

Flop: ($4.20) 6♦ 6♥ T♣ (3 players)
SB checks, Hero bets $1.12, MP folds, SB calls $1.12

Turn: ($6.44) 3♦ (2 players)
SB checks, Hero checks

River: ($6.44) A♠ (2 players)
SB checks, Hero bets $1.92, SB folds

Total pot: $6.44 (Rake: $0.29)
BB (Hero) wins $6.15

MP is 44/6/0 0AF passive fish on 37 hands, BU is decent nitreg, SB is 13/8/3 2 AF meganit reg on 170 hands.

The fish made a bit of a circus out of this hand with limp/call 3bet 30bb deep, nothing looks normal. SB must have had a much wider range to overcall, still a shitty spot for him OOP. He must have felt stupid. After he checks to me on that dry board I thought I just steal it immediately. I guess I have a bit of eq left on this board against fish range, B25 looked strong enough here for them I bet. And fish actually folded. Then SB x/c this though, which is super weird. I had no more idea really what he could have. Definitely, I saw no point in betting turn after he checks to me. River comes Ace and he checks again.

So now my hand reading goes like T9, TJ, 22-55, 77-99, JJ, KT, some QTs.
AK, AQ, AJ he should have bet on the river, I would mostly see blockbet here and I was totally ready to fold to any block. When he checked though... He just has so much small value that doesn't look very strong to him in this line. My check behind on turn is not a big deal I think. I could do this with some nuts even at this SPR and definitely I could have played AK, AQ, AJ, AT that way. I thought small bet probably looks actually super strong to him and of course I don't need much fold eq here to make this profitable. 23% roughly.

This time it worked out. Really not sure I should that bluff spot often though. Can someone elaborate please?