The Church has given us the answer to that question numerous times. When the Church makes an infallible definition, we can be sure it is Christ who is speaking.
I don't know what Poche's line of thought is, but for non-Feenneyites (I'm using Feeneyite here as a descriptor, not an insult) it might be possible to be inside the Church without being a visible member. Furthermore there's always presumably the possibility of a deathbed conversion, though of course that depends on whether you believe baptism of desire is a thing, I know some people here don't.
It seems conceivably possible to say what Poche said without denying any dogma. Whether that is in fact what's going on, or whether Poche is in fact denying dogma, I don't know.