In short: I'd expect it to be made primarily using a community-available bitsy development tool.
There's some leeway since, like, people have hosted their own extended bitsy editors, and plenty of bitsy games have hacks written into their html after it's exported.
I do think that it being made through a community-available bitsy development tool is kinda what delineates what I'm looking for when I use the tag, though. Like, if somebody wrote something up entirely in a totally different environment but it just had simple grid-movement and minimalist pixel sprites and tagged it "bitsy," I'd think that's misleading- kinda like if I were looking for RPG Maker games and somebody was putting GameMaker games on the tag just because they are turn-based RPGs. What unites the bitsy tag and the bitsy community, to me, is novel approaches to such a simple toolset resulting in such varied output. The editor is something of a rallying call to rise to an artistic/design challenge, and it'd kinda dilute the tag to include style homages.
But that's just my opinion! I'm not an arbiter of bitsy or its community, but I hope that perspective helps!