ʿUmūm al-salb means that the denial applies to each individual member.
كُلُّ إِنْسَانٍ لَمْ يَقُمْ
Every human being failed to stand.
For three individuals, A, B and C, the assertion is:
A did not stand.
B did not stand.
C did not stand.
It does not leave anyone affirmed as having stood. The initial kull distributes the denial among members; a vague translation such as ‘all did not’ hides the crucial point.