IDK, you'd have to ask him yourself.

What I was referring to was this plugin he made and gave a talk on in a past vim conference:

https://www.youtube.com/watch?v=Qnos8aApa9g

Harpoon is really cool, especially if you only work with 3 to 4 files. The ability to switch files with two keys is extremely nice. It's just a very ergonomic and pleasant plugin to use.

Looks like ThePrimeagen is one of the conference hosts/announcers