Legally there's very little HARO can do except force you to defend a meritless case. I don't believe they have a leg to stand on. You're not violating copyright, or trademark in any form, and he doesn't have an issued patent.
The one real takeaway is never launch a business and credit the competitor on the site. It just gives them fuel to create legal hassles for you.
Next steps: Get a lawyer. Have your lawyer write a firm letter showing Shankman's lawyer that their claims are meritless and you will vigorously defend the case.
Meantime, this is a great PR coup for you. Tech blogs love a little drama, at least certain ones do. Use it for the free PR.
Disclaimer: I am not a lawyer. Though I have had to defend against bogus patent and copyright claims before.