Sam just happened to be heading to the diner himself when he got stuck behind the crippled woman. Maybe she wasn't crippled permanently, but it didn't really matter. He watched her struggle with the door for a minute and then finally slipped around her.
"Here, I'll get that for you," he offered.
Without waiting for her consent, he edged his way around her and started to open the door for her.
It might have at least looked gentlemanly, not that he cared all tha tmuch about how it looked.