Ask me this,
How can Sony stop the DS4 from being connected to the PS3 and the PS4 at the same time when,
A) The PS3 doesn't know what a DS4 is, it sees a generic USB controller
B) The DS4\PS4 connection is the only wireless connection the DS4 supports
C) The PS3 never syncs to the DS4, since it doesn't know what a DS4 is.
The only way for Sony to prevent the controller from being working on both consoles at once is for Sony to prevent it from connecting to the PS3 and PC and the only reason it does that in the first place is due to the way USB works.
All of this doesn't matter. Yes, Sony can't do really anything about it anymore, because they fucked up already unless DS4 has the ability to patch its own firmware. Which may even be the case. The Wii U gamepad for example is patchable.
In any case they could have implemented functionality into the DS4 to avoid it.
USB is a protocol. Which means the DS4 knows, when it's just connected via USB and connected via USB including communicating over it. It knows, when it's not plugged in over USB, just plugged in and when there is communication involved.
Which means Sony could have detected it being plugged in and communicating with PC/PS3. And
then just not transmitting button presses etc over wireless during that time.
You may now complain about that behaviour and that you would want to plug it into PS3 to charge it while playing on PS4. For that case, they could have implemented an option, switchable on PS4, where PS4 sends the DS4 a special command to disable/enable USB controller functionality. Make that default to on, so that the user can turn it off in case he/she wants to play on PS4, while charging it on a device, that gets controller input at the same time. Would be pretty strange anyway, because the user could simply charge it using PS4 in that case.
This doesn't seem any different from a kid mistakenly getting hold of a controller and buying shit. A mistake? Yes. Avoidable? Yes.
I don't see it that way at all.
Noone pressed buttons at random. The person was actually playing a game on PS3 and the controller sent out commands to PS4 as well. That's like having a wireless mouse, which is sync'd to one of your PCs. And the mouse also has USB support. Now you connect that mouse to your notebook to buy something on steam. And instead of acting like a proper input device, the mouse sends your inputs over USB and to your PC at the same time, resulting in your buying something twice. I can't blame the user, especially when the manufacturer of the mouse didn't list this "feature" anywhere and also didn't warn him. I would blame the manufacturer.
It simply makes no sense for 1 input device to send the data to 2 consoles/PCs at the same time. There is simply no reason to do so. It's a design oversight. Errors happen. Manufacturer should simply fix the issue.