I would say that the quoted sentence from the Wikipedia gemmule article is wrong. The first sentence of the containing paragraph says:
> Asexual reproduction in sponges occurs via budding, either by external or internal buds.
At face value, the two sentences together imply that sponges can reproduce by external budding, but that the external budding "reproduction" does not produce "new sponges"(!). Note that the most recent edit to the article (on 10 March) was by an anonymous user who changed the sentence you quoted from "Both types" to "Only endogenous types", so this was a somewhat recent corruption.