Context, man, context.
In cell phone discussions, home service always refers to a carrier's own tower coverage.
Especially when given a map link showing ATT-specific cell tower coverage (NOT landline coverage) and the post goes on to talk about roaming outside of those areas.
And exactly how many average Joes know that? Not very many I would guess.
Disinformation is worse than no information at all, and people can find these threads through google!