That guy never uses paper towels, you know. Guess that makes him one of those eco-friendly types.
Literal
That-guy, absolutely paper-towels use-not [emphatic-んだぜ]. Earth [to-に] gentle guy [quotative-って] thing is, [right-よな].
地球に優しい ('earth-friendly') is a standard calque matching English 'eco-friendly' — the particle に marks the indirect object 'to whom/what' the gentleness is directed. Note the contrast between the admiring or mocking surface and the context: the speaker could be sincere or ironic, and Japanese leaves that ambiguity wide open. ~んだぜ is a casual masculine emphatic ending. ~ってことだ is the colloquial 'means that...' / 'I guess...' pattern — literally '(it) is the thing that X'.