Pat found out Liam was streaming Warframe, and as he really likes the game, offered some advice, etc. That tweet is from Matt's wife. Anyways, there are two options here.
1) Pat is really trying to extend the olive branch and Liam is being a complete asshole about it.
2) Pat really has no intention of making amends due to how things ended up between them and is just fucking with Liam by being "friendly"
We'll never know, because we'll never get details on what happened.