I've found what appears to be a fake paper in a non predatory journal
The first thing to do is to contact the editor at math reviews and express your doubts about the paper without making accusations of impropriety. Describe what you have found using neutral language. Suggest that others be enlisted to check further into the provenance and accuracy of the paper. 

If you are in your early career, it is especially important not to assert misconduct. 

You could also contact the editor of the journal in which the paper was published, saying you have serious doubts about the validity of the paper and, perhaps, that you aren't able to follow the citations. 

It is hopefully enough to shake the tree and wait to see what falls out. But do it in such a way that you can't be retaliated against, unless you have enough reputation to sustain you. 

Of course, it goes without saying that you need to be clear in your objections and to have carefully considered alternative explanations.