Newb question and I guess not all that important but just curious why this can happen, every explanation of counter hits specifically states it has to be performed during startup.
Edited to prevent confusion * better explanation below
DPs and certain other reversal type moves (Guile Flash kick, Urien EX head butt, Chun EX Spinning Bird Kick, etc) have been given a special property where they gain counter hit status on recovery.
These are exceptions to the rule. They added this exception to SF5 in an attempt to discourage people from using DPs irresponsibly.
But, you are right, USUALLY, a counter hit involves getting hit during the start up of your move.
This is false. Whiff punishing normal moves does NOT give you a counter hit. Only DPs and certain reversal type moves have counter hit status during their recovery.
Oh OK… Never paid attention to that.