And by extension, all users of FOSS must be the product, right?

I see it more like a question than a rule.

"The service is free. Am I the product?"

That is a valid thing to ask. Even with FOSS sometimes.

Some FOSS projects are backed by companies, then yes, plausible to ask.

Otherwise, I would answer with a clear no.

(Projects can still collect telemetry and other data and sell that, though the sell part should be very rare, imo...)

Edit: Was that a bad faith argument or a honest question?

Sometimes I can't tell, maybe because of old or ESL...

> all users of FOSS must be the product, right?

i would default to this being the truth, until demonstrated otherwise. Call it cynical, but it's the cynical that survive.