So what does this mean?
They rejected your request to submit more information for your application. Your application will be judged on its merits based on the information submitted at the time biometrics were taken.
I had requested them to share this info with the concerned ECO. I
don't know if they will.
They won't, thats quite clear from the answer you received, specifically this line:
After biometrics, you won't able to change any information and application will be under processing.
But can they still claim deception after I sent an email?
Possibly, but the email might be judged to be fair evidence that your mistake was innocent, and it also might not be. No one knows until it's reviewed in an appeal.
If it gets refused, can I say that I tried to disclose my mistake in my administrative review?
You certainly can, but whether it affects any administrative review outcome is not something that can be judged here unfortunately.
Edit to add (based on comment discussions): The OP has two choices here - proceed with the application and hope everything comes out fine in the end, or withdraw the application, amend it and resubmit it.
The merits of each are very different - withdrawing the application, amending it and resubmitting it has the lowest risk (no risk of a rejection because of missing information), but highest immediate cost in that they have to pay the application fees again (as they are withdrawing after biometrics have been taken) and no long term risk.
Proceeding with the application on the other end has a lower immediate cost (they've already paid the application fees for the current application), but higher immediate risk (rejection for missing information) and still higher long term risk and cost (a ban and the cost of mounting an appeal - which is far more than an application fee).
Even if the attempt to supply more information is taken into account during any appeal, there will be a monetary cost attached to that appeal which far exceeds the cost of withdrawing and resubmitting. Even a straight forward appeal can be costly.