Yes there was an error, the hotel (appears) to have quickly notified the guest of the error and offered an alternative. However:-

Offering 3000BHT off a 26000BHT room is pretty weak. My guess would be that these speciality rooms are rarely occupied and getting significant revenue from the room is much wiser than leaving it vacant.

If the BAR is 26,000BHT, it would have been win-win if a 50% discount was offered. That is, the OP could have elected to pay 13,000BHT for a suite normally double that - and maybe the OP would have accepted that, and if so, the hotel would be bringing in 13,000 BHT per night rather than nought.