On the balance, both of your accounts are new on HN - I can see both possibilities for this post of "I will rally the technically savvy in a false flag operation and nuke the person I stole from off the internet" and "I am informing my fellow community of something that is not right, looking for support / warning others".

However - your account does have one advantage in this: Codecanyon's project pages list the date the project was created on Codecanyon, not a date of the author's choosing. Additionally they do not make it simple to completely re-write some older project on there you might have already had to re-use the timestamp to mask devious deeds.

So far your timestamps win over his. Unfortunately, I still have no access to the code of your project to vet whether one is a copy of the other. Given that your code is sold for profit, it would be hard to verify this without your code getting out without going to trial (or I guess I could give you some bucks on codecanyon to find out what's hosted there).

Edit:

On review of the code in your live demo at https://pure.codeworks.org.uk/ I definitely agree he ripped you off. That's an unfortunate danger when it comes to selling client-side scripting. Good luck taking him down.