If you want to stick to a common set of definitions we can work from the Catholic defintion and compare that to the muslim definition (which I thought we were doing).
newadvent.org/cathen/07543b.htm
“St. Bernard defines it: “A virtue by which a man knowing himself as he truly is, abases himself.”
These definitions coincide with that given by St. Thomas: “The virtue of humility”, he says, “Consists in keeping oneself within one’s own bounds, not reaching out to things above one, but submitting to one’s superior” (Summa Contra Gent., bk. IV, ch. lv, tr. Rickaby).”
(note one’s supperior does not indicate Christian or non-Christian)
Another useful Catholic reference is the Litany of Humulity:
O Jesus! meek and humble of heart, Hear me.
From the desire of being esteemed,
Deliver me, Jesus.
From the desire of being loved…
From the desire of being extolled …
From the desire of being honored …
From the desire of being praised …
From the desire of being preferred to others…
From the desire of being consulted …
From the desire of being approved …
From the fear of being humiliated …
From the fear of being despised…
From the fear of suffering rebukes …
From the fear of being calumniated …
From the fear of being forgotten …
From the fear of being ridiculed …
From the fear of being wronged …
From the fear of being suspected …
That others may be loved more than I,
Jesus, grant me the grace to desire it.
That others may be esteemed more than I …
That, in the opinion of the world,
others may increase and I may decrease …
That others may be chosen and I set aside …
That others may be praised and I unnoticed …
That others may be preferred to me in everything…
That others may become holier than I, provided that I may become as holy as I should…
If we take these as the criteria of being “humble” let’s asks ourselves if a muslim, adhering to orthodox islamic teaching, would say these things in reference to non-muslims. I would say no on several of these.