It's not too unusual for Disney to call in extra buses from Mears** to handle extra traffic (and if too many of their own buses are out of service for some reason.)
What is ODD is that your MK bus dropped you at TTC. That sounds like a possible driver error.
Either that, or there was so MUCH bus traffic at the MK gates that they were using that method to move the overflow of guests via TTC that day.
**Mears has a transportation contract with Disney.
Mears actually operates all of the Disney Magical Express buses, too.