This is a good illustration of why so much encryption and extra security is often overlooked by users due to the complexity of setting it up and keeping things safe.
In this case @URUkL9tDXQLW5N8yg5F5 simply wants to verify that the signing key does, in fact, belong to you, @gaaned92, and he’s looking for independent verification (your email exchange is one - meeting face to face would be better for a key exchange).
I can second keybase.io as an option to simplify this a little bit, as it allows others to find you and see if you’ve verified yourself against many services and websites. For example, here is my profile on keybase: patdavid (Pat David) | Keybase. Where you’ll find my public key, along with my other verified accounts:
Really, it’s not simple and often confusing for casual users to setup and implement. 
I do like keybase.io though, as it takes some of the complexity out, and you can even encrypt a message that only I can read right on the site.