The PD applies to all civilizations, but is more permissive with those that are already capable of FTL travel. When a species is out travelling the galaxy, you can interact and negotiate with them, but you can’t directly interfere with their business.

Caleb is leaning hard into the “pre-warp” side of it, as many fans tend to do, which is why he said those particular regulations don’t apply. He’s just conveniently ignoring the rest of the PD, assuming it’s still in force in the 32nd century.

Edit: I’m wrong - I was conflating Caleb’s argument and the earlier debate about returning to pre-warp times. Caleb’s argument isn’t explained, and we funny get to hear what he’s saying immediately before.