Perhaps you have memorable wallet ?
As for main subject I agree that often I was surprised how deep their memory goes but I don't credit it to skills unique to Thai bar and massage boys.
I think people working in places with constant change of faces develop this kind of memory, it's why our teachers years after seem to remember at which desk we used to sit in class.
And by no means boy's memory is universal. Few years ago I offed guy from now defunct Adonis and he was my longest off ever possibly, from 10pm to noon next day.
Next trip , only 6 month later I met him by chance at barber at soi Twilight RIP and he did not recognize me at all, after while thinking I was his English teacher.
On another hand some are really half geniuses. My prize goes to Wes from Arena whom I offed LT to BBB Inn in Dec 2014. For him it was kind of milestone because it was his first time he went with client to client's place. Never saw him after until Jun 2018 so 3.5 years later and still he not only remembered me but also fact that we went to BBB Inn