We mentioned before how idiotic it was that Mattel released Dr. Fate and Guardian in back-to-back series, since they looked almost exactly alike. That was the entire inspiration for this Figuretoon, proving that it doesn't take much to amuse us.
If you want to create a backstory for this, go for it. Somebody's been stealing Dr. Fate's clothes from the communal superhero laundry room, and he thinks he's figured it out. There, done.
And for the record, Doctor Fate appeared in 1940 - Kirby didn't create Guardian until 1942, so maybe he did steal the costume!