It means you got lucky, you can dig the offshoot out and plant it in a dixie cup. Some Streps do put suckers on roots.

I.

Will it hurt the main plant of I go digging in the root ball? How much do I cut out?

It is usually enough if you get a little bit of roots with this baby - so you do not need to disassemble the whole rootball. Get the baby by the bottom with your fingers and gently wiggle and pull. I think you will be able to pull a half inch of roots this way. Get the baby covered with a glass or baggie to help it root - just keep it very barely moist.

Now - clean the soil from under the nails.

;-))