Usually, the term "Seized" means the crankshaft won't turn because something won't move. Usually because a piston is "stuck' in a cylinder and won't move. If that is the case, the flywheel won't move either.
Sometimes a motor will overheat due to lack of cooling..OR.. lack of lubrication. Then a piston will "seize" in a cylinder. Sometimes, when the engine cools down, the piston will shrink in diameter enough, that the crankshaft can be rotated again.
I don't know how the mechanic could
Induce the engine to seize using a socket and breaker bar. There must be something else going on...crankshaft main bearing failure..??
There are a couple of people on this forum who are more knowledgeable than I am..I think one of them is actually in the business.
Take it slow. Good luck.
NB