Clarify the behavior about event and property triggers

See the comment threads at [1] for the rationale behind the behavior.

[1] https://android-review.git.corp.google.com/c/platform/system/core/+/161601/16/init/action.cpp#232

Bug: N/A
Test: N/A

Change-Id: I8b271073ec14ad9fa9add5df60577b34d1df3241