I have seen that many a time. Truthfully if the batter swings you cannot be sure of the pitch speed. I have also had sensitive guns setup at short distance pick up the laces and not the whole ball giving very high readings.
Could be bat speed. I don't even consider that. Whatever the case, I feel pretty confident that our P didn't have an 8 mph jump in her speed on one pitch, which she has never been able to repeat - lol.