The documentation states:

"with tagged templates - any host problems created by triggers from this template will be marked"

https://www.zabbix.com/documentation/current/manual/config/tagging

Something like this would reflect the situation more:

"with tagged templates - any host problems created by triggers and any items created from this template will be marked"

Items also inherit Tags starting from 5.4, I have just learned today from a certain mister Addams. So, this should be reflected in the documentation.

This is one point where this is a bit unclear, but there might be more. For example, there is no use case detailing the template level item tag inheritance.