Motion Control is the broader subject that covers everything to do with the Super Knob, arpeggios, the motion sequencer, the Envelope Follower etc. Essentially, anything having to do with using the energy of one thing to modify or modulate another. Using Arpeggios as Side Chain Modulation sources is an example of such interactions considered Motion Control. The MC icon appears any time programming includes so sort of dynamic interaction via controller changes... be it Side Chain Modulation, Envelope Follower, Morphing, or a Motion Sequence.

The Motion Sequencer is one of the Motion Control functions. It consists of 16 programmable Steps. The Step, instead of being Note-on events like an arpeggio, are Control messages tied directly to any of 251 parameters within the synth engine. This means you can practically automate any parameter change with this programmable sequencer for Control messages. There are eight Sequences. Each is individually programmed and each can have unique target parameters. The Sequences can be set to Loop, or can be manually trigger as one shots.
8 Note driven phrases can be associated with any Part (Arps)
8 Control driven phrases can be associated with any Part (Motion Sequences).
The Super Knob can have 8 Motion Sequences of its own to automate its movement and control over the individual Part's Assignable Knobs.

You can think of them as programmable LFOs or as a programmable Envelope or simply next level automation. They can do panning, filter sweeps, pitch automation, etc., etc., etc., all simultaneously and individually scaled. Linear and non-linear control is available.