Logical thought process time! The zombie/them attack on tanya and the hospital happened in relatively close time period. The Army of zombies was to capture the hospital AND to kill off four of the baddest zombie-killers around. The attack on the tower/tanya is ONLY to stop anybody from the tower going to save the team at the hospital. Saul and Lizzy are irrelevant right now.
Here is why I think this is happening, Tanya said that the colony was attacked last week, we know that the zombies go against nature and attack the threats, they are working together now, finally Kalani and Angel killed THREE behemoths Burt is the best shot around and Riley knows how to use completely silenced weapons.
I still don't like Steven though. If the Rat isn't Kalani I want it to be Steven. And to anybody who is skeptical about Kelly having a gun, remember she is outside the tower in an unsafe area, I wouldn't want anybody there NOT to have a gun.