How often does he have a 6 here?

BB is the definition of TAG after around 50 hands. His flop bet here is way out of character for a Q. How often does he have less than a 6 here? His play made no sense to me for any other hand.

PokerStars No-Limit Hold'em, $0.25 BB (9 handed) FTR converter on zerodivide.cx


MP3 ($10)
CO ($17.80)
Button ($19.65)
SB ($24.50)
BB ($57.45)
UTG ($22.40)
UTG+1 ($58.90)
MP1 ($26.35)
Hero ($38.25)

Preflop: Hero is MP2 with 9:diamond:, 9:spade:.
1 fold, UTG+1 calls $0.25, MP1 calls $0.25, Hero calls $0.25, 2 folds, Button calls $0.25, SB completes, BB checks.

Flop: ($1.50) 6:diamond:, Q:heart:, 6:spade: (6 players)
SB checks, BB bets $0.75, UTG+1 folds, MP1 folds, Hero folds, Button calls $0.75, SB calls $0.75.

Turn: ($3.75) 8:diamond: (3 players)
SB checks, BB bets $1.50, Button folds, SB calls $1.50.

River: ($6.75) J:diamond: (2 players)
SB checks, BB checks.

Final Pot: $6.75