No. ATO means that the train is run automatically, with little human intervention necessary. It is what PATCO and WMATA (Washington) have had for a long time. ATO does not require a specific kind of signalling system - only that the wayside equipment must be able to relay signals directly to the train, so the train can decide what to do. It can be used with either fixed-block or moving-block signalling.
CBTC is moving-block signalling. To explain moving-block, I'll have to explain fixed-block...
With fixed-block, there are fixed sections of track, called blocks, that either contain a train or are empty. To maintain safe distance between trains, the signals are configured to assume worst-case scenarios - such as that a runaway train is hurtling toward a stopped train, and they are as close as possible.
CBTC (Communications-Based Train Control) makes those blocks move - so that instead of fixed sections of track, there is instead a moving "virtual block" behind every train. Each train knows the exact location of the train in front of it, so it can keep a safe distance. Furthermore, speed info is also communicated, so if a train is stopped or slowing down, moving trains behind it must slow down and keep a further distance away.
ATO without CBTC is no more efficient than old-style signals. Only CBTC brings the speed and capacity benefits. It can do that because it makes the whole system more intelligent, eliminating the inefficiencies of fixed-block signalling. The MTA is spending billions on this because it is the only way to increase the speed and capacity of the system without digging new tunnels, which always costs more.