How come this wasn't a split pot?

I was in a NL hand when 5 spades hit the board including the Ace. Thinking me and the other player both had Ace high flushes. The other player bet and then I go all in with no spades in my hand, but playing the board. The other player calls and wins the pot holding the queen of spades.

Why didn't we split with an Ace high flush on the board?

This was upsetting because I was in a stt with a good shot of winning and at least finishing in the money since the 4th place guy was barely hanging on with a couple of hundred chips.