Tapping out for something that doesn't disrupt them or protect me seems risky.
At competitive REL, the spectator would have received a Match Loss if guilty of outside interference - likely far more than any GPE penalty.
"It was your duty to stop him at the first card he was playing, YOU would get a game loss for that. Not him."
If there is cheating involved - say the OP could have stopped the starting player from casting his first spell but did not in order to see what the spell was - then the player involved is disqualified.
When you've said "you've just given me extra information" that starts ringing warning bells though, I'd probably pull you aside and have a chat...