My app login information is being opening in other user

Hiiii, I have created one dynamic App with login and Sign up system. It is one time login system. It is Google login & sign up system. My app is connected with firebase . First , I created an App, then I had download it , on my PC . Then, I just opened my app and Just Signed up with Google. Till now everything was going ok. Everything was working well. Then I had shared my APK to my friend . My friend downloaded the APK successfully . When he opens the App , my account was opened. Their he was not needed to sign up with Google , my account was opened in that App which I had signed up with Google

He probably has your account signed in on his device.

No, first of all I had just signed up with Google then I had shared my APK to friend

Don’t Tag text or typing email in you firebase database. tag your email in firebase authentication .