It would make alot of sense since considering that finding your friend (let alone anybody for that matter) will be on the planet. The game boast 18 Quintilian planets so.. they thought “Hey, it would probably be smart to not require Plus because of this”. “PS Plus won’t be a requirement to play online, however you will need to connected to the internet for your discoveries to register with the universal atlas,” a representative from Hello games said
Personally, while this is all fine and dandy I still wish they would work on a party system of some sort so that we could explore the planet together with friends. The games whole draw was because the universe is vast that multiplayer would be a more of a thing. Maybe they will add the feature later, though It would definitely move alot more units if it was there at launch.