700c, 28" and 29" are exactly the same size, just different names. They have been on the market forever.... I remember the 28" from the 1980s, Maybe not on an MTB-designated bike, but on what one would have said back then " normal bike", maybe labelled as hybrid these days. the MTB from the old days had the same geometry as " normal bikes" anyway.

Vintage is just a nice word for outdated.