After upgrading to El Capitan, OS X imported my email accounts from my iPad
More than likely, your Mac synced with your iPad and got data from iCloud. Go to Settings -> iCloud, and see if Mail is turned on. If so, and you do not want these to sync together, turn it off. Then, you can simply delete the accounts from the Mail app on your Mac. 

In regard to your question about other "surprises," while you're in Settings on your iPad, take a look around any other areas, such as Notes, Calendar, etc. that you may not want to sync to your Mac.