That behavior is a workaround in the event that the first name isn't set for a user in Google. Joomla requires that the first name field is set, so we have to get something to put in that field.
With that said, that code was written quite a while back and may not be correct anymore. If you'd be up for making a minor code change, it may get you going how you'd like right now.
I believe we could set that first name field to be blank now and just have the user's last name. There may be other options as well as the Google integration was written some time ago and the first name functionality may not be so limited within Joomla.
If you're interested in trying some options out, the following code change is where you'd start:
In the /plugins/jfbconnect/provider_google/profile/google.php file. At line 76, you should see:
$profile->set('first_name', substr($profile->get('email'), 0, strpos($profile->get('email'), '@')));
You can change that to:
This will try to use whatever Google responded with for the user's first name.
$profile->set('first_name', " ");
This will set the first name to a blank.
This will set the first to a specific value for all users.
We don't have a Google user that has this behavior.. ours apparently have first names.. but at the time we wrote that code, we had users who told us of similar issues, which is why we started using the first portion of the email instead to make things work.
I hope the above helps and is clear. If not, or you need assistance, just let us know!