The TM 6 forms where handed out during the flight. The airlines only responsability. They did not check if it was filled in. Not their duty. And since the governement clearly stated that there are support staff to assist with filing a TDAC at the airport in Thailand its clear. No involvement of the airline other then remind their passengers of this new entry requirement.
Who made this? Its not correct. No deny boarding because Thailand will assist at the airport, before immigration for those who did not file or where not able to file a TDAC.
"Passport holders of all nationals with residence permits in the UK/Ireland/UK territories can apply for the e-visa through Royal Thai Embassy, London"