If the article was published in a PubMed listed journal, it should ideally be listed in PubMed. You should first check whether other articles published in previous issues of the journal are listed in PubMed. You should also carefully go through the journal's website and check if there is some policy that might prevent your paper from being listed in PubMed. Some journals have embargo periods, that is, articles might be made freely available only after a certain period of time after publication. However, since your friend's article published in the same journal was listed on PubMed, this does not seem to be the case. If you do not find a suitable answer to your question, you can write to the editor and ask/him her about it.