Guide is telling me to destroy shadow orbs, but I have the Crimson

This is probably just a bug. If you have Crimson just replace 'Shadow Orbs' in your head with the Hearts (I forget their name) you see in the 'fingers' of the Crimson. I don't know what the purpose is for what he is telling you to do but for all intents and purposes Crimson and Corruption are the same thing pre-hard-mode and only slightly different in hard-mode.

This is obviously a bug... BUT if you or someone else has spread the corruption into your world from a different world then maybe you have some part of the world that is corruption. You can test this by asking the dryad if she says otherwise then it is a bug