This is what I could gather from various information sources on Myanmar's thermobaric bombs:
1) These bombs were either imported directly from China or partially or wholly assembled in the DI 21 factory from imported parts.
2) These bombs are manufactured by a Chinese state-owned arms company known as the China South Industries Group Corporation which first showcased them in 2015 before transferring production to Myanmar for the purpose of supplying the Myanmar air force.
Known as DI 21, the factory produces aerial bombs used for multiple purposes by the Myanmar military, including air raids.
Similarities between bombs produced in the DI 21 factory and other bombs manufactured and marketed in China South corroborate that their design is Chinese origin.
I have a couple of remarks on this:
1) the Fuel-air explosive aerial bomb showcased by the Chinese and in Myanmar looks different. Here are a couple of photographs of the Chinese 250kg Fuel-air explosive aerial bombs used in Myanmar (BTW these same bombs are also in use with the Pakistan Air Force)

2) the tail of the bomb dropped by the Myanmar airforce against the rebels in the province of Karenni, looks very much like the one of the larger Russian incendiary/thermobaric bombs (ZAB 500Sh, FAB-3000) - the Russian also support military the Myanmar regime.
3) A double red band near the nose of the bomb stands in Myanmar for High Explosive (but, as for Russians, thermobaric may be indeed classified as "high explosive"))