Many elementary questions about functions are given the "functional-analysis" tag. Consider the following examples, all of which are very recent: 1, 2, 3, 4, 5. This is not a recent phenomena; I've been noticing it for some time.
The confusion is likely incidental. Askers who don't know what functional analysis is are likely to infer that it's simply the "analysis" of "functions".
I believe that the description of the tag (i.e., the description that appears when you move your cursor onto the tag) should have some sort of warning.