No it’s meaningless. Biden and Trump will win plenty of states they never set foot in.
I think they mean that nobody is voting for Biden. I do think a lot of people will be voting for 'not Trump' though and they don't care who the other guy is so they won't come out to hear him speak.
In other words, his tiny crowds are not that important. This election is about Trump. If you love him, you vote for him. If you hate him you vote against him. Biden is just a dementia addled empty suit that they prop up on stage so you can vote 'not Trump'. And plenty of people will.