It's pretty hard to find a name that isn't already _something else_. Not impossible, but hard. Your tome.app at least isn't an editor, so...
I mean.
Tomedit. Tomale. Lots of words to play with.
and no real reason to if he likes the one he chose.
Considering there're many projects named tome in github (and not, such as the same named tomeapp.com) linked app has probably done some good marketing/SEO to come as first result in searches.