It means exactly what it sounds like. County "A" originally had a criminal charge against the person. County "B" actually located the person and held the person in their jail until they could make arrangements for the person to be transported to county "A." County "A" will then take the person to court in county "A" and the rest goes from there.
An out of county hit is police slang for a warrant issued by another county that was found in the computer system. Basically, the person was stopped, for whatever reason by county "B," they ran his name and personal identifiers (date of birth or social security number) through a computer system, and a warrant from county "A" popped up on the computer.