To quote you: 'he said it's self transfer. Which means he goes through immigration' - This is not necessarily true.
'collects bags' - Not necessarily true.
'then heads to check in for next flight' - not necessarily true.
'So he's got to fill in the TDAC arrival card' - Not necessarily true.
You made 4 statements, all of which could be completely wrong, that's pretty dumb. But then to try and defend what you clearly said you come out with a load of drivel. That's very, very very dumb.