It’s an extremely safe way of money transfer because you’re not leaving your banking information anywhere but your phone. When you initiate the google pay payment your banking information remains hidden and they also implement a lot of encryption and passkeys to protect your information from being stolen. Even if your phone was stolen, the thief wouldn’t be able to use it to pay with Google Pay because he would need to know your passcode and unlock your phone. Unless it’s a very small purchase in which case he could.