Accidental value bet! (dont bluff donks)

[ZoolooZ]

Had this insane hand where i read weakness on river as flush card came so i made an overbet bluff on river and the guy called. Was so anoyed cause i knew he had the straight and made a good call, then he muckes his cards. How can he call here, and bear in mind i hadnt been playing like a maniac.

Phew, have a look and tell me what a strange hand this was.

Poker Stars - No Limit Hold'em Cash Game - $0.10/$0.25 Blinds - 9 Players - (LegoPoker Hand History Converter)

SB: $10.05
BB: $20.15
UTG: $24.90
UTG+1: $23.90
MP1: $21.30
Hero (MP2): $19.65
MP3: $34.25
CO: $6.35
BTN: $72.10

Preflop: Hero is dealt 6[img]/images/graemlins/heart.gif[/img] A[img]/images/graemlins/heart.gif[/img] (9 Players)
UTG folds, UTG+1 calls $0.25, MP1 folds, Hero calls $0.25, 4 folds, BB checks

Flop: ($0.85) 7[img]/images/graemlins/spade.gif[/img] A[img]/images/graemlins/club.gif[/img] 8[img]/images/graemlins/spade.gif[/img] (3 Players)
BB checks, UTG+1 checks, Hero bets $0.75, BB folds, UTG+1 calls $0.75

Turn: ($2.35) 7[img]/images/graemlins/spade.gif[/img] A[img]/images/graemlins/club.gif[/img] 8[img]/images/graemlins/spade.gif[/img] 6[img]/images/graemlins/club.gif[/img] (2 Players)
UTG+1 checks, Hero bets $2.00, UTG+1 raises to $4.00, Hero calls $2.00

(i am now sure this guy has a straight, but he give such huge implied odds i know if i get my full house i am getting all his stack, admitadly this makes my river bet a bit stupid)

River: ($10.35) 7[img]/images/graemlins/spade.gif[/img] A[img]/images/graemlins/club.gif[/img] 8[img]/images/graemlins/spade.gif[/img] 6[img]/images/graemlins/club.gif[/img] J[img]/images/graemlins/spade.gif[/img] (2 Players)
UTG+1 checks,

(this flush card comes he checks week so i decide its a perfect time for a bluff)

Hero bets all-in for $14.65, UTG+1 calls $14.65

Pot Size: $39.65 ($1.95 Rake)

UTG+1 had 8[img]/images/graemlins/heart.gif[/img] 7[img]/images/graemlins/heart.gif[/img] and LOST (-$19.65)
Hero had 6[img]/images/graemlins/heart.gif[/img] A[img]/images/graemlins/heart.gif[/img] (two pair, Aces and Sixes) and WON (+$18.05)