How would the landlord know the ex husband’s name if it wasn’t on the lease?
I get calls from creditors for my ex-spouse, kids, ex-employees, whatever, they just call whoever they think they can pressure into sending a few bucks or who they can make so miserable they'll turn the screws on the debtor or even pay it off themselves.
I've had debt collectors tell me I was responsible for the debts of my ex-wife. They're just dirtbag scum.