Wrong, it's all about the lease he signed, if no animal are allowed or no snake , being a good tenant or not as little to do with what happen next.
Rules are rules and in the case of an apartment, property managers do not make exception they just enforce rules, last thing they would want is that other tenants hear that an exception has been made.
In the case of a house it is up to the owner but again it all comes down to the lease.
The good news is that eviction process is not as easy as the owner might think, the bad news based on the threat that was made, the owner can and is likely prepared to make the tenant's life a nightmare.
When you sign a contract you sign a contract.
To the OP you have a few choices but first you need to check your contract.
Sell your collection and stay where you live
Find a place to live that accepts snakes, and in that case you must be upfront with the number of animals also, in the mean time have a friend or family member care for you animals.