google device find locked a galaxy tab 8 at walmart
how are they going to unlock that device. 


Starting from Android 4.0 and up, when locking a device using find my device it will not give you the option to choose a password, rather when unlocking the device you will have to enter the regular password/pattern that was used on the device till now. Therefore, all they have to do, is enter the password they always used.

If however, there was no password till then, and when locking the device, you chose a password, then they will have an issue, and they'll probably have to use some other method to enter.


  Also anyone know of a way for me to kick that device off of my google account?


Being that your account was registered with a public device, I'd suggest you wipe the device using find my device. Just log in, and choose the option to erase everything on the device.