The 50 BMG is indeed powerful, but it is a far cry from a nuclear warhead. 50 BMG develops around 13,000 ft-lbs of energy at the muzzle, roughly 4 to 5 times what a 30-06 does.
50 BMG was not developed to shoot people, it was developed in 1920 to shoot the then-new tanks, and during the past 90 years it has done many tasks well (including shooting tanks). IIRC, a 50 BMG will shoot through 6" of armor plate or 13" of reinforced concrete.
Shooting a person with a 50 BMG will definitely ruin their day but will not necessarily dismember them, but it could break them apart if hit just right. Shooting over a person's back will not generate sub-molecular disturbances that will cause tissue to burst asunder and degenerate into their elemental state, although a person hearing it go by may void the contents of their intestines in hopes of trying to get a little lower in the dirt.
And finally, the 50 BMG was developed from an experimental WW1 German anti-tank round, and it is much closer dimensionally to a scaled-up 8X57 than a scaled-up 30-06. Not that it really matters, though.