would somebody please explain this to me?

Jackie Robinson (1951) hits a HR on a 1-5 roll. There is no HR on that part of the card (its either a triple or double) and the pitcher is not fatigued. The only potential explanation I can think of is that he hits a triple and then legs it out for a HR (but wouldn't that be recorded as a triple?).
J.Robinson 1-5 Home Run (CF) b-H F9
0 A.Pujols 3-9 Walk b-1 F9
0 1 S.Sosa 1-6 Strike Out b-0 F9
1 1 A.Belle 6-8 Strike Out b-0 F9
2 1 J.Dimaggio 1-5 Home Run (CF) 1-H b-H F6
SUBSTITUTION at P: Jack Townsend (role: Middle Man)
2 G.Foster 3-6 Ground Out (3B) b-0

You got it right -- he legged the triple into a homer, and of course it counts as a homer just as when you stretch a single into a double it's a double. Sometimes you see TRIPLE b-0, meaning your guy tried and failed to leg the triple into a homer...

thanks.

I assume your base running is set to very aggressive.

I assume your base running is set to very aggressive.

It wouldn't necessarily have to be if the outfielder in question was a noodle-armed clone of Johnny Damon.

In this case it was a "noodle-armed" Ashburn.