what was the right move here...

i was in a tournament the other night and we were about half way through with the blinds up to $500-$1K. first guy to act raised to $2K the guy right behind him raised to $4K (he had a huge stack)everyone folds around to me in the small blind. i go all in with $15.5K. big blind folds, initial raiser folds. next guy mulls it over and ends up calling for a little more than half his stack. i had pocket K's and he turns over A-4 offsuit. low and behold an A comes on the turn. and i am out.

my thoughts were, the initial raiser was short stacked and didnt think he had any thing decent, especially the way he was playing. the second raiser i hadnt had the pleasure of seeing too many of his hands since i was just moved to that table a few hands before this one. i put him on AK or AQ. so i feel i made the right move. two questions:

-what was he thinking risking more than half his stack with A-4. he had to at least think i had A-x since three hands earlier i went all in with pocket Qs.

-second, should i have waited until after the flop and risk the A coming up on the flop? i feel i could have scared him off if i did that.

thanks for your input. this has been driving me nuts.