Based on what I’ve seen, I’d say the seller is correct.
I checked Shooters Bibles from the ‘50’s, 60’s and 70’s which have Hunter fit charts and couldn’t find similar codes. By the 80’s - 90’s, they had dropped Hunter.
After looking at a number of Hunter spring type holsters, I believe I understand their code. See my photos with supporting examples.
The first number (33) represents the spring style holster. I’ve seen both “R” and “P” and it appears R is for revolver and P is for pistol. The next number is options/variations. 24 is plain russet, 25 is plain black, 29 has a safety strap and 30 is their shoulder holster. There are others.
The final number and letter represents the barrel length and size of the handgun. “2M” would be for a handgun with a 2” barrel and a medium size frame.