I think you might have confused the “challengers” and the “observers.”
The challengers are the ones that members of both state parties select and approve before the election to make sure the ballots are counted fairly/correctly. They’re about 150 in number and are in there with the ballot counters (along with lawyers from both parties) and watching the ballots, and are still there with the ballot counters at this point in time.
The “observers” are the people allowed outside of the room (there are windows allowing people to look inside), and it sounded like there might not really be a number limit (but I’m not sure). However, by state law, observers - unlike the Republicans’ and Democratics’ challengers - aren’t actually allowed to enter the room or interact with what’s going on in the room or the people in it. In fact, if they try both Republican and Democrat lawyers stop them immediately, and if they continue the police force them to leave.