Huge Weight Differences not Uncommon
I should say, or at least add, that it seems that these kinds of weight differences were not unheard of, and in fact may have been common. As Dieselnoi once said of the "yodmuay" of today, comparing them to those of the Golden Age, in the past a yodmuay would fight everybody. It's not just that the structure of greatness has changed in contemporary times, with a drastically smaller talent pool, or a mega gym like PKSaenchai hoarding all the talent, so that there are far, far fewer great vs great matchups (that, yes), but also that yodmuay of the past would not only fight all or most the elite fighters of their own weight class multiple times, they would also fight well out of their weight class vs champions well above them. Sometimes way above them. You fought everyone, and therefore, you lost. The year after the Samart vs Panomthuanlek size mis-match, you had Panomthuanlek's yodmuay brother, Chamuakpet fight Sangtiennoi. From available records, this was the 122 lb Rajadamnern Champion vs the 130 lb Rajadamnern Champion (leaping over an entire weight class, 126 lbs). Holy hell. with Chamuakpet winning (beating him for the 2nd time).
People ask, What made Golden Age Yodmuay so great? Part of it was that they were not only fighting in the greatest talent pool in Muay Thai history, even the 3rd or 4th best fighter in a weight class was a historic killer, when you peaked at a weight you went up and fought the very best above you, and even further above you again. You fought up until you hit a ceiling.