Theoretically, residue from vaping seems like a possibility. Anyone with a clear drip tip would know that. When I clean my drip tip, I notice that all that water indeed is slightly colorized to whatever juice I'm using - that's why it doesn't evaporate so well out of the drip tip even if it sits there forever. Do enough vaping in a car, like a ton of it, and sure, it may get a little filmy on a spot on the window. It's more based on temperature though, as temperature fog would probably have to first accumulate on the window, which would trap the vaping particles. In your house, fog would probably have to first accumulate on something to trap this. Otherwise, running a vicks humidifier would leave residue about a million times quicker, and in that case, ask your landlord if they'll pay your in-office medical bills since a vicks humidifier just so happens to be the only "at home" remedy helps you and your son with his asthma and your whatever. And if you want to vape, say it was a humidifier. There's nothing they can do to prove otherwise, and if they kick you out for something that they didn't witness and you didn't do, there's protection agencies for tenants - a landlord just can't kick someone out for being black or white, and if your landlord is a different race than you, you certainly have a civil case you can file for.
Trust me, if your landlord is this type of person, pretty soon they'll be telling you that you can't cook certain foods, bathe with certain soaps, or bring certain races of people into the house. If you give them an inch, they'll continue to take miles til they get to California. Pretty soon, they'll be telling your son he can't use an inhaler in the house - it's literally the same chemicals.