I had similar advice from the UK Embassy when my son had to enter Thailand in 2020 with a UK passport that expired in 4 months. The UK Embassy even tried to suggest that he need an Emergency Travel Document as he would be refused entry at the border. The advice I got on this Forum suggested otherwise, and fortunately I followed this advice and not the Embassy's!
He entered Thailand and was stamped in until the expiry date of his Extension, 1 month before his passport was due to expire, leaving plenty of time to get a new passport before then.
Embassies are probably issuing such advice over an abundance of caution, as some countries/airlines may require 6 months remaining on a passport, but Thailand is not one of them.