My take, FWIW:
If the child asks, you're not hothousing. Not ever. Even if you're teaching. After all, teaching a child who ASKS to learn is never a bad thing. It's really not! I'd hate for teaching to get a bad name when it's child-led!
If the child likes Starfall, asks to play it, then I feel very strongly that it's perfectly fine.
OTOH, if a parent is taking the lead because s/he wants to impress friends with everything the child knows, that's hothousing. IMHO, even *that's* only a problem insofar as 1) it isn't about what's good for the child but is about the parent's image, and 2) there's an opportunity cost of all the things a child isn't doing and learning while s/he's being flashcarded to high heaven (or whatever).
And of course, it makes people doubt what HG+ kids can do on their own. I'm with you on that completely!
The fine line with hothousing comes, I think, because sometimes the parents tell themselves they're trying to help the child to get ahead. But in hothousing situations, that usually goes back to wanting to look good to the parent's peers, perhaps just further down the line. Does that 4yo really care about going to Harvard in 14 years or so? If not, that's a parent's goal, not a child-responsive one. To me, that seems misguided.
In short, I think hothousing has little/nothing to do with teaching or not teaching; I think it's about what the parents' primary goal is. Is it to follow the child and help him or her to grow, or to lead the child so as to make Mom and Dad look good in their peer group?
I suspect people reading this forum are in the clear. In my experience, usually people who are hothousing don't think twice about hothousing!