Timing chains don't really break all that often, but the fact that it did immediately after the work performed simply is a coincidence that can't be stomached!!
At the very least the advice not to replace the chain was faulty, but something was done during this to cause the chain to break, ie: sliding off tensioner or some other issue. Proceed from a standpoint point of "what are yall gonna do about this".....

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John