If I understood the facts that you have set forth it sounds like though living in North Carolina he had a probation grant from Georgia with North Carolina supervising him. It is difficult to say what Georgia would do to him, however, it is possible that they may simply revoke his probation and let him serve his sentence concurrently with the one that he is serving in North Carolina presently. It may even be that this is exactly why he is now incarcerated. What he could do is try to contact his local probation officer and find out what if anything has happened with the probation he was on out of Georgia; is it still ongoing, or has it been revoked. If he can't find out that way, than he probably should simply contact the probation department for the court in Georgia where he was originally sentenced and see what if anything is happening with that probation order, or if it has in fact been revoked.
Based upon your description of what happened, it sounds like he was charged with a new crime as a result of the test in NC (pelad guilty, one year unsupervised probation and a fine). If Georgia has revoked his probation then he should have appeared before the judge that originally sentenced him in Georgia to learn his punishment (it is possible that was done in abstentia, but unlikey). If he has been revoked, there will be a revocation order filed in the clerk's office in the county where he was originally sentenced that will show what the judge ordered for punishment for violating his probation. If he has not been revoked, then his probation officer in Georgia can (and may have already) issued a probation warrant for his arrest for violating probation. If he is under arrest in NC, he may be waiting to be transferred back to Georgia. When he gets to GA he will be brought before the sentencing judge who will decide his punishment. The judge can revoke up to 2 years for technical violations and more for new felonies or violations of special conditions of probation. I cannot tell from your question where his new conviction would fit. The judge can never revoke more than whatever the balance of his probation is. So, if for example he only has 6 months left, that's the worst the judge can do. Finally, he needs to get in contact with his probation officer and the prosecutor (best if through an attorney) to see if he can work out a deal regarding how much punishment, if any, he should get for this probation violation.