Now that I've purchased, this is more a post-sales question, but... I saw a competitor just launched their upgraded site in the last 24 hours and they also switched to Xenforo, and I see some copyright info from "Waindigo", but I go to the linked site and I see nothing but a request to pay money for subscriptions to add-ons. And no add-ons.
Is Waindigo a person? Does this person make add-ons? Are they useful? Where do I find them?
You have an add-on installed that looks like it must be around 4 years old, and that add-on was authored by Waindigo. I'm certain that no one is going to "accidentally" go and pay for a subscription which, looking at that site, gives you nothing.
Copyright messages should always be left untouched unless you have the express permission of the author.
Is the add-on you're using still available here? Is it now under the ownership of ThemeHouse? If so, you should contact them. They can advise what to do to change/remove the links or upgrade the add-on.
I was under the impression it's something in base version of Xenforo because I always see it on my forum.
But now that you said it's addon related, I had a look at my addon list and disabled the "Import Tools by Waindigo", and this removed that copy right. I think this import tool was installed by the specialist I hired for the forum migration purpose. It's no longer needed.