They are worked up over it because they fought hard to get something which they want, i.e. a bus with separate seating. only to have this guy KNOWINGLY!!!! violate the code of conduct for this bus. this is not a halacha issue and do not turn it into one.
This was no different than an airline passenger with a kippa who stands up during landing to take out his bags with the seatbelt light on and everyone else sitting. Both publicly and knowingly violate the code of conduct. Whether you agree with said code of conduct is irrelevant, it is still a known violation.
It is also sad that Daniel could care less about the feelings of the other passengers. Putting himself before others