ORIGINAL: davidmil
You'll never know unless you can communicate with him. To say the wind and rain sent him running is pure conjecture. They live in the stuff. I'd say since the rain came from behind you and toward you and he left... he smelled you.
I am going to have to agree wtih DavidMil here, and since he is one of the more experienced members on this forum, you might want to listen to what he has to say or else you may have this happen to you again[8D]
Remember those summers when you were a kid? Hot summer day, then all of a sudden a cool breeze, then you can smell rain in the air. Happens often, since wind likes to blow out of a rainstorm, and into an area where there isnt rain (Isnt the saying wind blows from high to low pressure?). Hence, the reason you can smell the rain. That same wind carried your stench towards the buck, he smelled you, and bolted.
Also, quite possible he smelled a dominant buck in the area, and bolted.
Either way, the wind was the culprit!