You may wish to do some research into the various regulations governing the registration of local bus services. The services they have been operating since 2020 have largely been quite different from the E19, which is very much a ‘normal’ local bus service with numerous bus stops relatively close to each other.
It doesn't matter. It's registered as limited stop and it's not a traditional bus by virtue of how they accept custom.
As with any other registered limited stop bus, the E19 doesn't have to stop at every registered stop, but it must pick up there if customers want to board.
The way Ember know if somebody wants to board is the booking. It's very clear on all publicity that customers need to pre-book.
A traditional bus company would know if somebody wants to board by the punter sticking thier arm out.
That's the difference.