In this case God can very well call someone to be single permanently , for a all his life, without being a priest, nor religious for his sanctifiaction, it is obvious to me.
So in the sense that you have given, celibacy may very well be a vocation.
And still in the sense that you have given, marriage may not be a vocation for some who are married ( many get married only for their human happiness and not to become holy), even being a priest may not be a vocation for some who fool, and so on …