I am going to say something slightly different because I remember your other thread and the brief details you gave.
I would say that the typical behaviours which are considered "controlling" in children are reasonably common in 5 year olds, especially strong willed 5 year olds, who are wanting to have more control over their lives but still needing guidance. On that basis, is it likely that your 5 year old is showing both natural behaviours as per his age/personality, but also a great deal of stress because of the newness of the situation, the new school, not yet trusting you yet, etc, and his reaction to the stress seems like OCD or controlling, possibly? I don't know the specifics of his past obviously but many children from care will have been left to their own devices more than children in normal homes, and if this applies it will be very challenging to be in a more normal environment where the parent has more control.
Possibly rather than think about OCD, concentrate on the therapeutic activities which are known to help with trauma, and relaxing activities like massage or reflexology, and continue to get to know him, and keep on what you are doing, repeating what is expected in terms of behaviour and that you are there for him, and as he learns to trust you hopefully the behaviour will ease?
If you are really very worried about OCD then talk to a doctor, obviously.
The above is based only on my experience, which isn't extensive, so read it in that context!