Earlier quoted context omitted.
Stop bending semantics to fit your binary view point. Instant in this case means you move the brush and it distorts as you move the brush. No parallax, no beach ball waiting for it to do the computation. It happened as you moved it. It was instant. Even with brush sizes the size of the image you were using. It had unlimited undo. It had unlimited layers. That's not an arguable point.
Right, unlimited everything, got it. /me wonders why he even tries to point out the folly to people with no clue about how computers work...
Meaning they did not hardcode limits, and I assume had a O(1) or O(n) type scaling.