A lot of people call swollen lymph nodes " swollen glands" although this is a misnomer. Glands can't be swollen. Anything you know about " swollen glands" translates directly to swollen lymph nodes.
Lymph nodes are responsible for filtering crud out of the blood stream . YOur friend's doctor is a very, very bad communicator ( as a lot of doctors tend to be) and shoud have explained it better. This probably isn't the site to be , but i've had the lymphnodes under my arms swollen ( which always happens when I use underarm deodourant directly after shaving/ waxing my armpits) . They usually go away after a few weeks. Sometimes ( very rarely) cancer can get into the lymphatic system and that's very bad because it spreads all over the body. It's unlikely that that's happened in your friend's son's case ( and she/he would have mentioned it if it was a risk) , so don't fret about it.
Usually they just hurt / feel funny for a few weeks and go away. I think it's usually caused by the lymphatic system being clogged up as a result of being unable to cope with the amount of infection/inflammation they have had to cope with.
Hope that helps. My A+P prof does a lot of research on the lymphatic system, so we've studied it a little, but I'm also not an expert. YOur friend should ask the doctor for some more info, and maybe going to " webMD" or another medical site will give you better information.. I haven't seen a great deal of medical experts in this room.