Welcome to the forum, tarouza!
Deltamac is a company from Taiwan, but they also have a lot of Hollywood product distribution rights for Hong Kong...and I believe Malaysia, Thailand, etc.,...perhaps even mainland China.
What is the region code printed on the back of the box?
JSDVD.com (Taiwan release) and YesAsia.com (Hong Kong release) indicate that the show is coded for Region 3...if the Thailand release is from Deltamac then that is Region 3 also (and seems to be NTSC not PAL). At the same time, it could be a bootleg copied from the Asian releases. Really tough to know for sure.