What Engels calls "metaphysics" roughly translates to "un dialectic"
Maps to what we’d today call essentialism about “natural kinds”, the reification of analytic distinctions, and static/snapshot thinking as opposed to process thinking (can’t understand a glider (GoL) by looking at a snapshot).
His reasoning: classical metaphysics since Aristotle tended to analyze being through fixed essences and rigid categories, so he labeled that whole static/categorical habit of mind “metaphysical.”