Can replacing catalytic converter cause cracked exhaust manifold??

Took my 2004 Toyota Corolla in and had the
catalytic converter replaced. Got it back and the
engine sounded "fluttery" and could now smell
fumes. Took it back and was told the exhaust
manifold had a crack in it and it would be another
$200 to weld it up. Pretty sure the engine noise and
the smell weren't present when I dropped the car
off. What's the likelihood the crack came about
while the catalytic converter was being replaced?
Would that be unusual, or not? Repair shop did not
acknowledge any responsibility for the crack.