You are right to feel cheated, IMHO.
This "Business Class" is actually very easy to spot - just don't book any flights on TG A320 and you are safe. Those planes are operated by Thai Smile and feature EU-style C product, which is indeed a disgrace.
TG lost my business on some routes when they started to operate those with Thai Smile, since I do not appreciate Y seat being sold to me for C price.
Regards,
El Puerco Volante