First, let me say that if one perceives what they follow as being spiritual, then it is to them. Second, there is a big difference between religion and Christianity, bigger perhaps than between spirituality and Christianity.

Here is Merriam-Webster's definition of spirituality:

spirituality

Main Entry: spir·i·tu·al·i·ty
Pronunciation: \ˌspir-i-chə-ˈwa-lə-tē\
Function: noun
Inflected Form(s): plural spir·i·tu·al·i·ties
Date: 15th century
1 : something that in ecclesiastical law belongs to the church or to a cleric as such
2 : clergy
3 : sensitivity or attachment to religious values
4 : the quality or state of being spiritual

and the definition of spiritual:
spiritual
3 entries found.

spiritual[1,adjective]spiritual[2,noun]spiritual bouquet


Main Entry: 1spir·i·tu·al
Pronunciation: \ˈspir-i-chə-wəl, -i-chəl, -ich-wəl\
Function: adjective
Etymology: Middle English, from Anglo-French & Late Latin; Anglo-French espirital, spiritual, from Late Latin spiritualis, from Latin, of breathing, of wind, from spiritus
Date: 14th century
1: of, relating to, consisting of, or affecting the spirit : incorporeal <spiritual needs>
2 a: of or relating to sacred matters <spiritual songs> b: ecclesiastical rather than lay or temporal <spiritual authority> <lords spiritual>
3: concerned with religious values
4: related or joined in spirit <our spiritual home> <his spiritual heir>
5 a: of or relating to supernatural beings or phenomena b: of, relating to, or involving spiritualism : spiritualistic
— spir·i·tu·al·ly adverb
— spir·i·tu·al·ness noun


When I speak of being spiritual, it refers to the supernatural, which was all created by God.

Yes, there are atheists that consider themselves spiritual.
I suspect you are referring to these in the strict senses of the words, yet anything one does with fervor and earnest for self edification could be considered their "religion" don't you think?

Are you seeking something specific for your own edification and knowledge here on this esthersvirtue???