From the description, I thought the system went like this…
There was a netmf app / Gadgeteer app on the 'bot, that looked on serial port for commands (this was created by Lars or someone else, not the students… that’s what the “appropriate firmware was developed” comment implied)
There was a Scratch interpreter on the PC that generated commands and pumped them out the serial port.
The bot and the PC were serially connected (xbee, CDC, whatever)