BMW Z3 ABS Faults? Query

[Mark in Ireland]

A mate of mine at work wrote his Z3 off on friday coming to work. He was doing 40mph in a straight line when in his words, it was as if the handbrake had been pulled on, the backend of the car spun round, he tried to correct the skid but the car skidded off the road and hit 2 road signs! The car behind stopped and said all he saw was a massive cloud of blue smoke and the back end spun round.
I asked whether the gearbox has seized and mu mate said he started the engine which ran perfect and put the car into reverse and drove backwards off the smashed road furniture. He didn't try going forward though. Could the abs system get a dodgy signal and apply one or both of the rear brakes?
I'm at a loss of what else could have caused the back wheels to lock up without any warning? Could the diff have seized?
Any ideas gratefully received.
Road was dry, don't know what gear he was in but can find out.
Cheers,
Mark

[TheEnd]

If he had ASC+T there might be a slight possibility, as that system can individually brake wheels by itself, if it was the ASC traction control, then no, that just throttles the engine to cut power.