Yes, it's a used as a developer, but as is common in many cases when replacing chemicals with other chemicals -- similar chemicals have similar properties. And in fact, some BPA-free thermal paper use BPS for example.
The question is who is reputable. Even when buying from a well known store, I don’t know how they audit their suppliers, because the paper is bound to be made by some company I’ve never heard of.
Yeah I would assume that given how easy it is to start a new Amazon seller account and how impossible it is for some random seller in China to face legal repercussions from the US, the likelihood of finding an “_____-free” item to actually be made of whatever the cheapest and most readily available formulation is. (Including the _____), is pretty high.