It's a bit more of embarrassing if you're the Sass consultant and the client is the one bringing it up. At least, that was what I gathered from the article.
I don't think there is any shame in learning from clients. In effect, whenever you talk to a client about requirements, you are asking them to teach you about their problems domain. As a consultant who develops things whether web sites or software, your value to the client is not in the completeness of your prior knowledge, but in your ability to execute upon their requirements and deliver the solutions that they need. So if they can teach you the occasional technical trick, this is just fine.