From the Standford Encyclopedia of Philosophy:

9. The ad verecundiam fallacy concerns appeals to authority or expertise. Fundamentally, the fallacy involves accepting as evidence for a proposition the pronouncement of someone who is taken to be an authority but is not really an authority. This can happen when non-experts parade as experts in fields in which they have no special competence—when, for example, celebrities endorse commercial products or social movements. Similarly, when there is controversy, and authorities are divided, it is an error to base one’s view on the authority of just some of them. (See also 2.4 below.)

https://plato.stanford.edu/entries/fallacies/

The point the parent was making is that citing authority isn't a bad thing to do. Citing authorities in _a different field_ often is, though.

(Citing a doctor on the common cold is not a fallacy, but citing a doctor on global economics is)