Probably an anomaly. Had a friend 45 how had a max of 265 on a ride. Turns out it was some sort of static interference with his jersey.

On a different front, I've had 500' of elevation change recorded on my Garmin 305 while riding on a flat road when a cold front passed, and had max MPH spikes (60 mph - I wish) for no known reason.

Fact is there are factors that can influence any measurement and throw it off.