Bank randomly visited home & took pictures

One of my friend's bank employees visited his residence and took pictures of him, his house, electricity meter & street. He got very scared, what could be the reason they did that? Tax issues or something else? Is it even ethical for them to show up without any notification?

EDIT:- no loans EDIT 2:- Apparently his bank account was frozen and they came to resolve the issue. He told me that it's now fine, so it seems like they were genuine employees but still does not seem to be ethical this way