There were stories that he wasn't a very good house guest. Didn't clean up after himself or his pet, wasn't very hygienic himself too. Don't know if they are true but wouldn't surprise me to be honest.
Being a guest to a somewhat sympathetic host, then getting thrown out for failing the house rules on hygiene (cats, condoms,...) seems to be his thing.
If he was such a terrible guest why is the old consul going out holding press conferences in his defence?
"Stories" is a good descriptor for unsubstantiated claims made by the Ecuadorian government, which were denied by the former president.
They might be referring to the fact he had a cat, but then I doubt people fumigate all apartments where the previous owner has a cat. If that had been the case then cat ownership would carry a bit higher rent.
I have heard that Assange let his cat shit everywhere and didn't clean up after it, FWIW. Perhaps that's what the comment was referencing.