I am not going to get into the discussion around the "boomer shooter" name, but surely HL1 would be considered part of the Gen X experience.

The youngest millennials were in their early teens in 1998. The last members of Gen X were finishing up secondary school in 1998.

I say this as a relatively early to mid generation millennial born in the late 80s.

The whole generational cohort approach can be very limiting. IMO late cohort Gen X and early-mid cohort Millenials have a lot in common.