"Each" and Targeting
To quote 114.9a, with bold for emphasis:


  114.9a Just because an object or player is being affected by a spell or ability doesn't make that object or player a target of that spell or ability. Unless that object or player is identified by the word "target" in the text of that spell or ability, or the rule for that keyword ability, it's not a target.


That really seems as straight-forward as possible. Does the spell or keyword rule use the exact specific word "target"? No? Then "it's not a target". The only other thing I can think of that may help is to show them gatherer rulings from any number of cards. Look at any card with Overload, for example: Cyclonic Rift, Blustersquall, etc. Both of these have Gatherer rulings that specifically state "If you pay the overload cost, the spell won't have any targets."