"You're cappin' bro no way this isn't moving"

Put your mouse cursor near the edges of the circle and see if it ever gets further or nearer from it, then tell me your mouse curson is lying too.

Like the old chocolate bar illusion (where you can slice a chocolate bar in a way that gives you an extra square), this is deceptive.

The color shifting can indeed trick your brain into seeing the illusion of motion. The way the dots aren't changing all in the same direction helps with that.

However, things are moving, ever so slightly. It's only a couple of pixels but it's there. Throw it into Photoshop so you can see each frame individually, greyscale it to make it easier to see, and then throw some guides on the circle. The circle moves only a pixel or two, enough to make an already convincing illusion absolutely undeniable.

So of course it looks like it's moving. It is. The expansion part in particular makes the circle wider by about two pixels on each side before snapping back, and it does it more than once to sell it.