There is a difference between "following one's own advice" and trying to give a (I am assuming constructive) critique. They may be able to provide good insight without necessarily having the skills to do it themselves.
General anatomy could potentially be a good example:
Personally I have a relatively thorough knowledge of human and animal anatomy from studying medicine (both human and non) but don't have the skills yet to fully show/apply what I know to my images.
Depends on their definition of "mistake" X'D I mean, if an artist deliberately makes the eyes on humans big as a STYLE, there is really no point in pointing out "hey, the eyes are too big" 'cause that was done on purpose X'D
So if the critiquer can clearly tell what is done on purpose and what is not, I think I'll be cool with that o3o
IDK like..sometimes it's hard to tell, imho. Especially if an artist doesn't have consistent style (like me hurrrr) Then you really don't have any reference basis for the critique and can accidentally point out mistake that is deliberate style quirk...the real question is, was the critique wanted in the 1st place (I mean I don't seek it out, because I know that every pic will be drawn differently so I won't really follow it). >.>
I think it depends on the tone and nature of the critique, but I voted "Nope" because you don't necessarily have to be able to do something yourself in order to see when someone else is doing it wrong. For example, someone might be terrible at drawing perspective in their own art, but they can still look at another person's art and see when the perspective is off. Sometimes it can even be more helpful to get advice from someone who isn't an expert in the field, because they come to it from a fresh perspective!
Also, it can sometimes be difficult to notice flaws in your own work because you stare at it for so long while making it that you just become adjusted to it. But when you see a completed artwork by someone else for the first time, the flaws can be more noticeable because you're seeing the final product all at once. So someone critiquing another artist's work may simply not have noticed the same flaws in their own work because the process of watching it come together hid the flaws from them.
On the other hand, there are certain kinds of critique where it should be easy to take your own advice. Like if someone says "you use too much green in your work" but they use a lot of green themselves, that's pretty hypocritical because you can make a conscious decision not to pick green if you think it's overused. I mean, unless you have a colour vision deficiency, but I think I'm going off on a tangent now . . .