Regular CRT televisions weren't multisync - at best they'd be able to deal with both 50Hz and 60Hz inputs, but they wouldn't attempt to sync to anything else.
Multisync means the CRT will succeed at syncing to multiple specified frequencies.
There is nothing stopping non-multisync monitors (including TVs) from trying to sync to an out of range signal and depending on the design they might damage themselves trying.
There is nothing stopping non-multisync monitors (including TVs) from trying to sync to an out of range signal and depending on the design they might damage themselves trying.