I'm no expert in YC's business, but I think the confusion might be coming from thinking about this too similarly to how later-stage investment works, where there are fewer investments to place and more information available, and therefore more up-front analysis. It's not feasible to do that in YC's case, where they fund hundreds of startups a year. Nor can such analysis apply anyhow—there's too much uncertainty at the earliest stage.

The way YC looks for signal is different: simple and rooted in a few fundamentals. Do the founders seem effective? are they talking to users? and so on. The funny thing is, even though the fundamentals are simple and have been laid out in pg essays for a decade or more, it's surprisingly hard to reason with them. The mind doesn't like to stop with so little. I think that's why YC funding something like this feels paradoxical. (In the present case, it wasn't what they applied with but something they came up with later; but that helps make the point.)

"Bait to get acquired" would be considered a negative, since that's not how a business like YC ends up with the few big successes that make or break it. It's more like this: is there some plausible random world in which this thing ends up becoming a major breakthrough? It doesn't have to be probable, just fairly imaginable. And the founders have to seem like the kind of people who might, with luck, pull it off.

(Sorry for editing the carpet from under you! What I just wrote here was in response to your pre-edited comment too, but hopefully is still relevant.)