I never heard it called tree town. The wayback machine page for the Wikipedia citation only says "Tree City USA", which is a thing the Arbor Foundation does for lots of towns.
So either the citation is out of step with the original page or a goofball put that in Wikipedia.
I think it has to do with the name 'Arbor' [1] than the town itself, which has a fair amount of trees in the older neighborhoods but isn't excessively forested.
So either the citation is out of step with the original page or a goofball put that in Wikipedia.