Does your son know the coach? Have they spoken before prior to this invite or did the DM arrive out of the blue? If so I would say it's a generic invitation.
My son dealt with many of these with polite responses stating he is interested would like to attend but travel may be a problem and see what kid of response he got. Sometimes they disappeared, sometimes it initiates a legitimate dialog with a coach.
Best case it would get the coaches attention prior to the camp so they know to look for his like baseballhs mentioned.