Can you address this point made in Matt’s post: “This explicitly contravenes the GPL, which requires attribution and a corresponding GPL license on whatever you release publicly built on top of GPL code” (emphasis mine)?

Matt also mentions in the comments of his post:
“When you embed and use GPL code, you have to release the entire thing as GPL. (That’s why it’s called a viral license.) So they need to release not just their changes to the editor, but the entire app that was distributed.”

You mention attribution in your response, but you haven’t touched on the licensing of your own app (which seems to be a main part of Matt’s argument).