Thank you for explanation. The source of confusion was Weld reference documentation, in particular

https://docs.jboss.org/weld/reference/latest/en-US/html/events.html

In section 11.2, there is

"An observer method need not specify any event qualifiers—in this case it is interested in only unqualified events of a particular type. If it does specify qualifiers, it’s only interested in events which have those qualifiers."