Question: How are people getting passive + Skill Tiers?

In [this video](https://youtu.be/EP8sPBiOaZc?feature=shared) for an Umbra Initiative build the creator has + 2 Skill Tier while wearing no skill tier core armor.

Is there something I am missing that gives passive Skill Tier? I'm a new player and this would allow me to realign two of my pieces of gear to do + Weapon Damage instead for my Capacitor build.

Edit: Fixed link