In a casino I believe the dealer would have asked for clarification on his bet. It could be taken either way as "I put you all-in", as in a 2800 bet, or as purely an all-in.
At any tournament table I'm playing "live", if someone makes a questionable verbal declaration, I will ask them to clarify their bet, whether or not I am in the hand. That way there's no room for debate.
Were you correct in the ruling? Eh.. probably not, it seems to me his *intention* was to put the small blind all-in, not to risk all of his chips. If you were at the table, you definitely should have asked him to clarify his bet.