This is very odd, yes Qatar denied him boarding because he had done two exemptions already. No he’s trying to get a tourist visa, change his flight and enter by train from Malaysia.
I know, there’s no official statement from the immigration regarding this. But we know one guy got denied at the airport in London last week because he had already done two visa exemptions in twelve months, even though he had a return ticket within 30 days.
This the updated website from the Thai Embassy in London. There’s at date no official specific restriction regarding entries by air, but there’s a general restriction that states just two entries on visa exemption by any means. This is not correct and there’s no official statement from MFA supporting this.
Formally it’s two entities by land in a calendar year, and there’s no formal restriction or limit on entries by air. But sooner or later you’ll get pulled aside and questioned, told to find a visa and/or get denied entry.