Barter within primitive communism was literally a very early stage of commodity production, advancement and generalization of which turned into capitalism.

The act of exchange already implies a degree of private ownership (as in, whatever is being bartered isn’t part of the social stock that’s free for the taking if needed), there might be traces of value present within the exchange (i.e. equivalence of trade subconsciously measured by something as to prevent trading a single berry for a stone chair) and yada yada.

It wasn’t capitalism because goods were mainly being produced for different reasons, but the act of barter was definitely a development towards commodity production, and by extension capitalism - after all, it’d be absurd to think that it came out of nowhere.