You can find in that thread pretty much everything you need to know about taxes and what you need to do to reduce or eliminate (depending on where you live) those taxes.
To sum it up, if you go to your account settings, jump to Tax Information, you’ll find there a W8 form. As you haven’t filled out that form yet, the IRS assumes that you’re a US author who hasn’t completed a W9 form and obligates Envato to withheld 28% from all your sales.
If you fill out that W8 form without a tax ID number, you’ll have 30% withheld from US sales only. If you provide a tax ID number, because you live in Canada (as I can see on your profile), you’ll be completely exempted from paying US taxes.
I hope this helps 