If you use /u/ instead of the dropdown box you get an instance agnostic link. eg /u/[email protected]
You're in lemmy.zip, so the link you see will be https://lemmy.zip/u/[email protected], which keeps you in your own instance so that you can message them, etc.
Just typing @[email protected] without selecting from the dropdown box does not create a link.
Yeah they need to tie it all together. Dropdown box links should be instance agnostic, typing @user@instance should create a link, and all user links should ping.