I had this issue too. The control center was opened after turning on the Apple TV. To me it seems as it is caused when a wake up signal is sent via HDMI CEC to the Apple TV while the Apple TV is already powered on.
I use a universal remote and the Apple TV is connected to a Yamaha receiver. In my setup the remote would turn on the TV, receiver and the Apple TV and then activate a so called "scene" on the receiver, that would cause the wake up signal on the HDMI. Since at that point the Apple TV was already powered up, the (then unnecessary) wake up signal caused the control center to open.
I changed the macro of the universal remote to not activate that scene. Thankfully, the Apple TV will still power on (actually I am not sure how this is done, since the remote is IR only, but I won't complain ;) ) and the additional wake up is not sent any more. Therefore, the control center is not opened after turning everything on.
I think this behavior of the Apple TV is a bit strange. I don't know if this is on purpose, but if not, it should be corrected.
In the mean time maybe others that see the same behavior can check if they also have something that sends a wake up signal via HDMI and see if they can disable this to work around this issue.