It's a bit more complex than that.
Basically, it is several channels multiplexed and all transmitted on one channel, yet constantly being switched between various channels.
That sounds confusing so let me explain what I mean.
Let's take as an example of a classic four channel RC system. You'd have roll, yaw, pitch and throttle. Each control stick axis is on a separate channel electronically, but then they are multiplexed together into a single channel and the receiver will demultiplex them back out into their various control channels so that each can move a servo or signal a microprocessor.
In the case of a DSM type transmitter this single multiplexed channel is encoded so that a single receiver alone (the one that you bind to) can understand your transmitter. This allows several users to coexist all in the same 2.4GHz band of frequencies. The fact that several users are all transmitting signals to their own vehicles at the same time potentially leads to interference problems and so the transmitter now uses frequency or channel hopping algorithms in order to avoid the interference from all the other users nearby.
So here we have used the word channel to refer to several different things:
- several channels, one for each dimension of control
- a single multiplexed channel of info transmitted to the receiver
- signal hopping between various channels to avoid interference
RC controllers have evolved through many generations and are quite good today at allowing numerous users to coexist in the same area.
Sure, you could design a transmitter that sends all the information you want on a single radio channel as this person seems to have done. But I think that they would soon learn of the shortcomings of their design if they tried to use that one design on multiple vehicles at the same place and time.