لَمْ يَكُنْ كُلُّ ذَلِكَ
Not all of those things occurred.
Here lam yakun comes first, and the intended meaning is the denial of complete inclusion. It does not logically imply that no event at all happened.
If two events took place and the third did not, “not everything happened” can still be true. Some occurrences remain possible.
Compare “nothing happened” with “not everything happened.” The first denies each item; the second denies the whole set. Treating them as the same proposition creates a genuine error in meaning.