I assume the OP meant BCAPL even though he said BCA. (Those two organizations have different rules.)
Here is the BCAPL rule:
1-40 Deliberate Foul ....
c. Object balls: It is a deliberate foul if you intentionally stop or deflect any object ball that is in motion, or intentionally move any stationary object ball that is in play, by any method other than a legal shot, including by intentionally contacting or moving any part of the table in any way. (AR p. 91)
Penalties First violation of (c): your opponent may have the object ball restored (if it was stationary), pocketed or left in its position after the foul. However, it is loss of game if it is the game-winning ball, if any deflected object ball contacts any other ball, or if more than one ball is moved.
According to this, because the ball intentionally touched was the game winning ball, it is loss of game. I think there is no ambiguity here.