The boy may or may not have been relieved about not going skydiving - I have found that super-sporty people are often totally blind about how other people see their 'exciting' pursuits. I worked with a group of young women who went on a river-rafting experience & were very apologetic about not inviting me too since I was also friendly with them all - I was so relieved as I would have said 'no thanks!' & then felt bad - it is very hard to get this type of thing right without complete straight talk. Always just say what you mean, ask first if in doubt, and try to be courteous to other people's views. Hope they eventually patch up their differences because it's obvious this mother was really just terrified at the idea of her son 'floating in space' ! Me too ! 
She is going to 'lose' her son soon anyway, so she should try to make herself 'put him down' psychologically, just so that she can  relax as he grows into a man. Remember - 'let them go' & they will come back to you - they do !!!