Is Full Metal Panic Fumoffu canon?

I'm currently binge watching the series and just started TSR. In the first season, Souske was under cover as a high school student and only Kaname knew he was really a soldier/mercenary.

In Fumoffu, they threw that completely out the window with souske pulling guns on people and shooting and all sorts of other crazy things. Everyone at the school seemed to know all about how he was Kaname's bodyguard and he was a soldier.

I was fine with this as Fumoffu was a wacky side story. But, now that I've started TSR, it seems that has stuck, and everyone still knows about him, as (in the second episode) he pulled a gun on a teacher. So, does that mean all the stuff in Fumoffu was canon?