$1/$2 NL Cash River Call Ruling?

[TexBigSlick]

$1/$2 NL Cash "Home" game.

We'll join the hand on the turn:

<ul type="square">[*]Player A: "Check"[*]Player B: Says "$30" and puts $30 in the middle[*]Player A: Says nothing and puts $30 in the middle[/list]Action moves to the river:

<ul type="square">[*]Player A: "Check"[*]Player B: Says nothing and places $45 -- three stacks of $15 each -- in the middle[*]Player A: Says says nothing, but places $30 in the middle[*]Dealer: Says to Player A "You need $15 more, the bet was $45"[*]Player A: Pulls his chips back and says "I thought he said $30, I fold"[*]Player B: Objects[*]Host/House: Rules that a fold is allowed. Host's reasoning was: Preflop, when players call $2 when a $5 straddle is out they are allowed to fold instead. This is the same thing.[/list]
How would you rule?