I don't have any hobby activity through my professional email address.  There are plenty of ways to make anonymous or semi anonymous email accounts to use for hobby activity.  

True story:  I kept getting LinkedIn requests from a clergyman in the north suburbs a few months ago on my anonymous account.  After a little investigation it turns out that the email address was coming from a fellow hobbyist with whom a had exchanged offline information with a few weeks earlier.  I guess hobbyists come from all walks of life.

It seems that if a person isn't careful with their LinkedIn settings it will scan your email contacts and send out invites.