Also, in the chat show that follows the show - The Talking Dead, Steven Yuen was not a guest on it when usually when a main character dies in the walking dead he/she turns up on the show. Also, the host of the talking dead never explicitly mentions Glenn being dead and rather opts to say things along the lines of "it looks like Glenn is dead" which alludes to things not being as we might seem.
They're not doing a very good job at trying to make us believe Glenn has really died.
Another thing to note is that Rick might be having his hand taken off just like in the comics, since the cut he has could very well be infected.