No, Scopus did not choose not to index your specific paper. Such decisions would undermine the purpose of an index.
There are three reasons a paper may not be indexed in Scopus (or Web of Science or SciFinder etc.):
- The paper falls outside the index scope (journal is not indexed (or was not indexed at the time of publication), paper type is not indexed).
- The paper will be indexed; however, the process is not instant, and it has not happened yet.
- For some reason, the paper has been missed. (I had a paper published once where the entire journal issue got missed by Scopus and WoS, somehow.)
To check whether your paper should be indexed, perform the following steps:
- Check that the journal was indexed at the time of publication. (Instructions for checking Scopus coverage here ; instructions for WoS here.)
- Check that sufficient time has elapsed for the paper to be indexed. The best way to do this is to look for newer content from the same journal. Once that appears, you can be certain your paper has been missed somehow.
Once you're sure your paper's been missed, you can complete the appropriate form to have missing information added to the index. Scopus, here; WoS, here.
A similar procedure can be followed for all curated indices/databases, but not for black-magic voodoo databases like Google Scholar.