It's not Glenn.
Glenn is a major character in The Walking Dead comic. He's sitting outside Atlanta right now with Rick Grimes and the rest of his group. Rick's group doesn't leave that camp until the start of winter, or at least just when it's starting to snow outside. A little over three months into the ZA, where we are at the end of Episode 3, and they are all still there near Atlanta. He isn't anywhere close to Savannah, and no one from the comic ever is.