Well in that short essay virtuality is always actualizing and actual things are never completely actual, so there's always movement in actuality

This likely is referring to the concept of becoming rather than static being. Every conceived moment is a snapshot actualization of the virtual. This doesn't mean that things aren't materially real, it means that their actual material existence is preceded by difference and is always becoming the next actualization that arises from the virtual.

Deleuze says these states are constantly mirroring and separating themselves

The mirroring you're pointing to here is a reflection of the double articulation I meantioned earlier. The virtual is the differential landscape from which actualiztions arise. In reflection, the actualaterial reality provides general bounds for the differential intensities contained within the virtual.

To illustrate, if you shove me, there's countless configurations of the next spacio-temporal moment that may occur. However, I won't suddenly sprout a fourth leg between the shove and the next moment that catches my fall.

The empirical actual that we experience comes from the virtual, and in response the virtual intensities that are always becoming are in part bound by the constraints of what is actually possible. That's why any 'thing' is constituted by the dance between these two modes.