Well considering the human only uses a fraction of our possible muscle strength, people can be born without the inhibitions in the brain to prevent us from over straining our muscles.
Without the said inplace inhibition, a person would have a ridiculously short temper, have seemingly inhuman strength, and a, ahem, huge appetite for carnal pleasure =P
Some of the things like him drinking butter and etc might be bull, but I dunno about the horsepower, it might be a typo, and some of it is him playing it up...
But 280 horsepower would be enough strength to drag a train or an entire plane, and people can and have done it.
So I think he could be that strong, but some of the stuff they say is played up. Things like him going berserk if he tried doing a feat of strength are highly highly probable, and he would have a huge thirst for sex and food do to his bodies overcompensation with energy...
I'd say 70% fact and 30% exaggeration...