The trigger event doesn't have to specify "creatures" entering the battlefield. For example, Captain Storm, Cosmium Raider from the Lost Caverns of Ixalan release has an ability that says "Whenever an artifact enters the battlefield under your control, put a +1/+1 counter on target Pirate you control." If an artifact creature enters the battlefield under your control, that ability won't trigger. If a noncreature artifact enters the battlefield under your control, the ability will trigger.