1996 Millenia S Smoke?? Help Please!!

Hey, Im a toyota guy but now im buying and selling cars. Anyways, i gotta 1996 Mazda Millenia with only 107,000 miles last night. I love the acceleration and everything. No obvious leaks or whatnot. Oil looks clean (amber), runs smooth.
Heres the problem... As i was being followed on the highway by a friend tonight, he said it blew some black smoke as i was accelerating.
Is this normal in a supercharged car?
Could it be because i put 10 dollars of midgrade when i'm supposed to be running premium. I tried to rev it in the parking lot and no smoke. Exhaust smelt clean...
Whats up with that "puff of black smoke"? Please help me, im getting paranoid and i like the car to keep for myself!!!
Thanks guys!

also, i just read that these cars can have bad supercharger seals that could cost up to 3000 to fox. Could this be my problem, how would i know??
HELLLPP should i keep this car?????

Supercharger leaking, thats your problem!

its all good now. prolly bad batch of gas...
;)

mine does it in high rpm's only in between shifts.