I suspect it has to do with someone bragging about qualifications of someone else, and not backing that up in any way. Makes the braggart look rather lame; asking for qualifications is one way of pointing out the lack of substance behind the brag. Most people over 50 understand that. Even some under 50 do, too.
Gargantua was implying that she and her husband know just WAY more than I do about what penance is because her husband was edumicated by Jebbies, clear through graduate school. She brought the question of education into evidence and used it to try to impeach what I was saying.
It seems to me if evidence is brought in in an effort to impeach, the evidence can rightly be examined. She introduced the ad hominem. Stand by it; fall by it.