Say whatever you want, regardless of whether you think I'm 'splitting hairs' anytime I see someone say warframe is 'f2p' I always want to say 'aside from slots' because they are not free unless you get a plat drop from watching a stream, please tell me under what description is something free that you have to trade for? That is my opinion on the matter and I genuinely think 'this game is f2p, if you ignore slots' because absolutely anything else (not cosmetics) can be farmed for. So you hypothetical example there being no plat in the market to trade for is basically one of the game having failed and thus irrelevant for the discussion at hand.
Obviously free to play economies depend on not everybody playing for free, someone has to pay the bills.
What they mean by 'free' and what everyone else understands is that you can play the game without ever putting any real money into it.