sorry, but surely if youre a mechanic, wouldnt you have gotten it towed straight home? why did you take it to another mechanic?
oh, cams cant 'slip/spin' as they are located by the retaining bolts.
if all the bolts snap, I suspect the gear would drop off.
possible you have a split boost pipe?
as already mentioned, skipped teeth(timing belt jump) on one of the cams.
had this happen to me.
timing belt idler collapsed on start up.
low on comp.
new belt and pullies.
and it was fine.
you were driving, so hopefully no internal damage.