[rainsford]

You're not wrong, but you'll also notice I didn't mention any specific email encryption protocols, deliberately so because the question was about general use-cases for signatures that don't reveal the public key used to create them, not whether any particular protocol is susceptible to such an attack. Certainly you can construct a protocol that preserves signer privacy, but the point is that you have to take extra steps to do so because it's not an inherent property of the signature algorithm. And I think the point of the article is that a naive implementation of signatures might not account for that fact.