The problem is in the perspective. Imagine a person with a very unhealthy lifestyle giving sound, correct, health advice. While the advice itself is correct,

The problem is in the perspective. Imagine a person with a very unhealthy lifestyle giving sound, correct, health advice. While the advice itself is correct, the fact that this person lives a very unhealthy lifestyle shows that the root of the problem is somewhere else. Ad hominem is about the logic of an argument. The parent said something quite precise - "[she] is pretty low on the list of people Ill take climate change advice from" - he didn't say that she's wrong. I totally support that argument. There are surely plenty of people with a significantly lower global impact, that can give advice that is correspondingly more effective.