User blog comment:PUNCHURPREGNANT/Gray and Silver Predictions/@comment-135.0.27.38-20140111155246/@comment-7418318-20140111170412

A "man" smelling like a woman is bound to stick to Natsu's memory better than a woman smelling like a woman due to being out of the ordinary.

Also he was giving chase to Zalty, through half the temple, so he had a lot more time to memorize the scent than when angel was just fighting someone else nearby.

Furthermore he was in close-combat with Zalty, but Angel never got all too close to him. If she was upwind on both occasions he might not even have picked up her scent at all.