Strange Move

[sjay2k]

My friend, A, was involved in an interesting hand against player B.

Before the flop, A raises (3x BB) from the BB and B calls the raise from the button.

Flop is Qc, 10c, 3h. A checks, B bets (5x BB), A calls.

Turn is 2s. A checks, B bets (5x BB), A says "let's see if I can suck out on you" and calls.

River is Jc (putting Qc, Jc, 10c on the board). A checks, B says "bet." Then A instantly (and excitedly) says "all-in" before B even says what he's betting. B looks incredibly confused, thinks for a few seconds, puts the minimum bet into the pot (5x BB at this point) and mucks Q-J face up.

I asked my buddy (A) and he said that he had pocket 9s.

What do you think of the play on the river?? Is it even legal?