You have asked me about the statement that I made regarding being a landlord is a social science. You have done a fantastic job for being a landlord. It is an engineering for which you need to know something about the house structure (civil engineering), electric (electrical engineering), plumbing (mechanical engineering), etc to maintain your rental properties and deal with contractors and handyman.
You need to know something about finance and investment which will help you to gauge the economic environment in your area, valuate/buy/sell rental properties, understand the potential renters credit history, etc.
The most important is social science, which includes communication and psycology. How to select a potential renter, how to deal the renters, how to solve any issues in the rental properties and raised by your renters, just like what you described in your post. Great Job! Always enjoy your posts.