Both of our kids are now in their 20's but they had some incredible melt downs growing up. A teacher of one of our kid's told us that when kids turn 12 - 13 a switch turns in their brains and they are able to start to think more like an adult. When they have emotional difficulties, they also start to deal with them differently. Typically the crying fits start coming to an end.
11 is a little old to met down over not being with his mom. I could see it to some degree if both parents left him with you, but you said the dad was with you. Kids melt down over some unusual things, and it may not have had anything to do with being with you or missing his mom. Mom being away could have merely been the trigger. As frustrating as it may be, the only thing you can really do in this type of instance is let the kid get over it himself. If you get angry or lose your temper with them in the middle of the melt down, it will make things worse. What we usually did was put the kid in a room by himself or herself and let them know that they could come out when they were ready to behave as we expect. After a while, they got over it.
Hopefully you will not have to witness something like this again.