Hello! Do you by chance know what the fault code was for? Did they write that on the invoice at all or mention it? Without knowing exactly what code was set, its hard to give any type of advice.
Traction control is mostly a function of the Anti-Lock Brake System, with some engine interaction. Shouldn't have anything to do with the transmission, so I suspect its not related to the traction even you experienced, but more of a coincidence.
If you could find out what code was set (maybe find a new mechanic!) I would be able to give you more assistance.