Glenn isn't supposed to die yet.
Think about it. In the comics negan kills him with baseball bat.
Now think back
When Rick meet Glenn the survivors come out with baseball bats to kill walkers.
Glenn is initially wearing baseball jersey and hat.
When Glenn meets Maggie for the first time, she rides in on a horse and kills walker attackig andrea with a baseball bat>more baseball bats and Glenn throughout show.>with the termites, Glenn is next up to be executes, in which they are preparing to incapacitate him with a baseball bat and slit his throat.
In another episode around that time, Glenn picks up a baseball bat.
Tl;Dr. Glenn must die by baseball bat, aka Negan.
The walking dead knows he's going to get killed but they dramatically induce it in tons of episodes, only for it to not happen.
This is just the icing on the cake before he dies.
GLENN IS STILL ALIVE, HE WAS THE BEST CITY RUNNER OUT OF YHE ENTIRE GROUP, WALKERS CAN'T AND WONT KILL HIM. A HUMAN WILL.
-Sincerely, a walking dead fanatic.