The rule is real, badly stated, and has a condition attached that almost nobody includes. Nothing you did was damaging.
What acid actually does. Seasoning is a layer of polymerised oil bonded to the iron. Acid attacks that layer slowly, and once it is thinned or breached, the acid reaches the iron itself and dissolves a little of it. That is what people mean by damage.
The conditions that matter, in order:
Time. A quick sauce of ten or fifteen minutes is essentially a non-event. Hours of simmering is a different proposition. Forty minutes is in the fine range.
How good the seasoning is. A thick well-built layer resists this for a long time. A new or patchy pan is exposed immediately, which is why the same dish ruins one person's pan and not another's, and why beginners get burned by the advice being absolute.
Leaving it in the pan afterwards. This is the real one, and the one the rule should be about. Simmering for forty minutes is fine; leaving the sauce in the pan overnight is where pans get stripped and food picks up metal. Cook, then get it out.
What damage looks like if it happens: a dull grey patch where the seasoning has gone, and a distinct metallic taste in the food. You saw neither, so you are fine.