Rent seeking is commonly defined as seeking to extract economic gain without contributing back a benefit. Whether you like the project/funding approach or not, it doesn't seem to fit the accusation of "rent seeking".
[0] https://github.com/feross/funding/issues/7#issuecomment-5245...
Rent-seeking is a term with a specific definition [0] and "I need to pay my rent" isn't it. In simple terms, rent-seeking refers to the behavior of the landlord, not the behavior of a tenant. It may even be a term that applies to this situation, but the dev saying they need to pay their rent is entirely unrelated.
A landlord is seeking compensation for a mutually beneficial transaction ("you get shelter; I get money") and is providing value to the tenant.
If I block off a river and charge you a toll to pass, I'm rent seeking. If I dig the Panama Canal and charge you a toll to pass, I'm not rent seeking.
By looking through the ongoing discussion, it was interesting to find a reference to the core-js issue [0] from earlier this year. Its maintainer, with his established position in the npm community, makes use of a similar post-install script to open up a discussion and communicate his situation. This gives him a more direct communication channel to its users without directly helping his situation.
What I assume can be understood as a rent-seeking practice, is how fooreys intention, with the same political power in maintaining a popular package, seems not to be solely to raise awareness to his situation. But instead he's forced a solution to his problem by advertising unrelated 3rd party products. Whereas he interestingly also uses the term experiment, it did already render npm as a space for advertisement.