theres a small wheel inside the big wheel. When that turns, it spins the smaller omni wheels (similarish to how orm gears work). As it shows in the video, there is only 1 main wheel that is surrounded by smaller omni wheels. There is a smaller wheel or gear wheel inside of this, when that turns the omni wheels turn. Also when the main large wheel turns at the same time it allows diagonal travel.
(I wonder how long it takes to get used to the travel and stop bumping into walls and stuff?)