Look at the URL you just posted, above. Go on, page up and look. Please note, between the "3p0." and the "gz" is a
t.
It's possible you like to argue, but I believe it more likely you made an error when you saved the file, and changed the file name.
If so, feel free to ... rename the file correctly.
A discussion of how pkg_add selects file names is in the pkg_add(8) man page, but the definitive logic is in the perl script itself:
$ grep gz /usr/sbin/pkg_add