Yes Strep G is contagious to humans and can be passed from human to human.
If you're positive for Strep G then you should avoid contact with other humans because you're contagious with Strep G until you no longer have it.
If you do have Strep G then you should avoid going to work or school until the Strep G is no longer infecting you.
Strep G is most commonly found and lives on animals such as horses, cattle etc and can spread from the horses and cattle and other animals to humans.
So if you do have a horse or cattle that test positive for Strep G then you should be very careful around them.
It's rare that humans get the Strep G from the animals but it's also very possible.