Good catch, but this "snafu" has been known for years.
Here's what http://en.memory-alpha.org/wiki/The_...de)#Continuity
has to say about it:
Clark Gable, who was by no means a leading man in 1930, was not the original choice of reference. The final shooting draft of this script has Edith reference "a Richard Dix movie", but the crew on the set felt Dix's name wouldn't be familiar to viewers in the 1960s.
So, evidently, there was a little poetic license involved.