I find that anybody who uses the term mansplaining loses credibility. If others opinion becomes disposable to you due to their gender identity, then you are a sexist.
Mansplaining is a particular activity, an obnoxious one. The "man" part of the term is in reference to men being far more likely to engage in it.
"Mansplaining" is not equivalent to "[a] man explaining". There's another term for that: "explaining".