I went back through the pictures which are still up on the auction site at the link given. The car is promoted as a 1951 Kaiser 4-door sedan, NOT a Traveler (although the car is a hatchback) and the body serial number shown in the photo group is for a 5121 model which was a 1951 Kaiser Deluxe 4-door sedan. The body serial number is consistent with 4-door sedan production. I suggest you check the build numbers given in KFOCI HANDBOOK Version 5.0 (on CD).
It has been my experience over 45+ years with these cars that it has happened where an owner or restroation shop has lost the original tags and slapped something else on the car to take its place. I am guessing, based on currently available evidence that this is what happened here.
There is a "but" to this. As is pointed out at various points in the Handbook, there were an unknown number (expected to be under 7,500 cars, all series and body types total) of leftover or work-in-process 1951 Kaiser cars that were re-tagged and re-worked into 1951 "Kaiser Virginian" automobiles, with "Virginian" or "Traveler" fender script, continental tire kits (optional on all models but Travelers) and in many cases, two-tone paintwork. These cars have door-post tags that have 1952 previxes and start with a "1" with the original serial number as the other group of digits. when the later series 1952's came out (different tail lights, 1 piece windshield, different horn button, etc) theyr door post numbers began with "12" and started at "1" (as in K521-1200953 for the 953rd Kaiser of the deLuxe series). Consult your copy of KFOCI HANDBOOK (I am assuming you are a club member) on CD (Version 5.0) show production counts based on all the factory monthly production statistics available when the version was released. by series and body type. It will explain the situation better.