Are the Tech Accounts set to receive notification when a client updates the ticket?
Under Setup > Techs > Techs > tech-account > Account Info
...in the Notifications section: Send me an email when... A client updates my ticket.
Is the E-Mail going out to the CC contact, what is ticked within the recepients section of an example Ticket? You are using WHD12.5.2 ?
If you have put them as a CC and the option is still enabled to go out to them, the update from the client should go to them too.
If you want to confirm the cause you can check the Ticket History; it is highly likely that you will see the email went out from the client just after they updated the ticket, which would mean the CC'd users are being notified because they've been left enabled in the ticket rather than an Action Rule or trigger event causing the issue.
If you don't want this to happen you should be able to un-tick the CC option and when the ticket is updated again it shouldn't go out to them.