Buckle fractures do not look like regular fractures. As I said earlier - my DS1 could still do certain things. It took me all day to decide to bring him in - we got in at the last appt time of the day and I really thought I was being over-cautious. Sigh.
When DD broke her arm, I even had her lay on the couch for 20 minutes or so b/c she is so prone to over-reacting. When we knew for sure that she wasn't over-reacting (poor thing had a concussion too which we figured out on the way to the hospital) we high-tailed it in. But with a regular fracture/dislocation we caught it much faster - it was totally different. It *looked* broken - her arm was a weird shape, which I hadn't seen right at first. It was nothing like DS1's arm - her forearm was U-shaped whereas DS1's arm was normal looking and still half-working.
Each situation/child is so different that we make the best calls we can at the time. You did make a perfectly good call - most likely the next day you were better able to deal with having two kids with you. It's unfortunate that it took so long out of your day but at least it's all taken care of.
Sending lots of healing vibes to your DS! Hopefully it's starting to feel better already!