That's not a list
Are you sure? "Learning Perl 6th ed", p. 46 says:
A list literal (the way you represent a list value within your program) is a list of comma- separated values enclosed in parentheses. These values form the elements of the list. For example:
(1, 2, 3) # list of three values 1, 2, and 3
This behaviour is documented (see the link I gave)
Binary "," is the comma operator…
In list context, it's just the list argument separator, and inserts both its arguments into the list.