This is Wikipedia, which is as good as most other definitions: Rent-seeking is the act of growing one's existing wealth by manipulating public policy or economic conditions without creating new wealth
¹ We’ll just assume that homesteading is impossible these days.
They could've bought up the land and house and not improved it at all and depend on the housing crisis deepening for increased resell profit- but they did not do so, they maintained this house I'm in and ensured me and future tenants can continue enjoying this place. That's not rent seeking.
All these things involve renting out something to fill a temporary need.
when you buy a house with the intent to sell it for a profit, then you are driving up housing costs. i'd say that's even worse than renting it out.