I would interpret it as anyone is welcome. The only barrier to entry is an internet connection, and even that is needed for just part of your experience.
I'd guess it's context is the censorship seen in the last decade on most social media platforms.
"Welcome" is in the eye of the beholder. Everyone can join, but I am sure as it is also with our real worldwide community, not everyone is welcome or is accepted equally.
But the point is, nostr does not intent to judge that. It happens automatically while communicating. Nostr is just the means to communicate.