Is this call read dependant?

Villain is unkown
His river bet just screamed bluff at the time.
Is this a good or bad call vs an unkown?

PokerRoom No-Limit Hold'em, $1 BB (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

MP ($48.00)
Button ($53.00)
Hero ($107.10)
BB ($105.50)
UTG ($38.70)

Preflop: Hero is SB with 9http://www.flopturnriver.com/phpBB2/...iles/spade.gif, 9http://www.flopturnriver.com/phpBB2/...iles/heart.gif.
3 folds, Hero raises to $3.5, BB calls $2.50.

Flop: ($7) 8http://www.flopturnriver.com/phpBB2/...iles/spade.gif, Thttp://www.flopturnriver.com/phpBB2/...es/diamond.gif, Thttp://www.flopturnriver.com/phpBB2/...iles/spade.gif (2 players)
Hero bets $5, BB calls $5.

Turn: ($17) 3http://www.flopturnriver.com/phpBB2/...es/diamond.gif (2 players)
Hero bets $10, BB calls $10.

River: ($37) Khttp://www.flopturnriver.com/phpBB2/...miles/club.gif (2 players)
Hero checks, BB bets $28, Hero calls.....????

Final Pot: $93

I think this is an easy call. Even versus an unknown.