You posted "3 yards or less," so yes, you can assume the "4 yards or more" number from that. Unfortunately, your numbers were incorrect. The correct numbers are:
199 rushes for <=3 yards. (50.6%)
194 rushes for >=4 yards. (49.4%)
Yes, that's pretty much exactly my point. When you're way behind, runs are a surprise and tend to go for more yardage per run.
However, I just checked the game, and my hypothesis was wrong. After his first carry (which went for 2 yards before he fumbled and SF returned it for a TD), Murray ripped off a series of long runs on the next drive. He also had some long runs later when we were down by 3 scores, but it's true that on our second drive, he ran for 9, 7, 6, 5 and 6. I don't know what defense SF was in, but I suspect they weren't expecting us to run consistently (we never had before, after all).