Yes, that is a Daniel Johnston quote on this Sunday's Mary Worth.
Possible explanations for this:
Okay, so there aren't any possible explanations for this. Mary Worth and Daniel Johnston are as different as two people can be, and that's without taking into account that one of them is imaginary. Let me break this down for you.
As you can see, I ran out of things to say about Daniel Johnston. He's just a good dude who makes wildly uneven music. Not like Mary "On the Morrow I'll Come for Your Youngest Child" Worth.
Possible explanations for how I saw this that don't involve me being a fan of a soap-style comic about a 60-something busybody whose megalomania is such that she believes every human is an empty vessel in which she can deposit her overflowing virtue:
Okay, so there aren't any other explanations for this.