Wikipedia would not accept it, the things are not notable.

Wikipedia does not bill itself as a datastore about everything, but rather only about the important things.

Also the data they store about each thing, is not everything about the item, but only the most important things about each item.

A lot of people have issue with this: After all, it's not like they are going to run out of space. But nevertheless, that is what they do.

Must it be one or the other?

This. The author of this webapp/service should consider leveraging Wikipedia for the "things" in a curated way.