I'd be willing to bet that we all find ourselves on the wrong end of similar encounters, where we feel we can talk with authority on a subject we actually know fairly little about.
There's even a name for it: the Dunning-Kruger effect.
This more or less says that people who are incompetent (in skills they are actively involved in) are likely to overestimate their competence. Their incompetence tends to make them unaware of the limits of their competence.
Conversely, so say Dunning and Kruger, people who are highly competent tend to underestimate their competence. Because they understand their field well, they are acutely (and perhaps overly) aware of the limits of their own understanding.
Of course, this effect has been folk knowledge for years ("the fool doth think he is wise, but the wise man knows himself to be a fool" - Shakespeare). However, Dunning and Kruger experimentally demonstrated the reliability of the effect.
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