Re Helios 522, this aircraft
- kept climbing despite the cabin pressure warning going off, and there was radio communication to the effect that not all was well > no communication of this sort here, apparently
- was intercepted when contact couldn't be established > didn't happen here (and I'm still asking myself why)
- had a history of pressurisation problems > doesn't seem to be the case here.
I think this comparison can be laid to bed.
What did the Thais see on their (military) radar? If it took up a western course after initial contact was lost it would have at least skirted their border with Malaysia or even entered Thai airspace. And the "200 NM NW of Penang" seems very close to Phuket in Thailand.