One thing though - the alien captain had certainly heard of it.
"Genesis allowed is not, is planet forbidden" IIRC. So there was a definate Federation "Keep Out" warning there. That is unfortunately one of the plotholes - they forbid anyone from going there, but only had a small science vessel, in orbit of the planet, to enforce this "no-fly zone."
If not a requirement of the script, Starfleet should have at least posted a couple of ships there to patrol an exclusion-zone around the planet.