Google as initiator of a DDOS attack. Is this possible ?

Maybe.
You all know this large public transport networks in the big cities. Thousands or hundred thousands people are using an underground, a tram or train each day. And manny of them have a smart phone with Googles OS Android. And you know the public address system. On each corner a loudspeaker is installed where user can be informed if there are some delays.

Now assume somebody hacks this system during rush hour and shouts into a microphone

“Ok Google call 911”

What will happen ? Hundreds or thousands of Google phones will dial the emergency call number 911 at the same time. The telephone lines of the distress call centre will be overloaded and real emergency calls get lost.

My recommendation: Make sure the phone is not ready for accepting a command (dark screen) or switch off the function “Ok Google”. At least when you are using public transports. So nobody can complain you were part of the attack against the distress call.