erm, not sure which law you read!
Firstly, the currency makes no difference, its where the goods were delivered to. Nor does it make a difference if the goods or services are for business purposes or not. If XenForo Ltd is VAT registered and the buyer is based in the EU, then they have to charge the buyer VAT. If the buyer is outside the EU, then they don't charge VAT. VAT is only charged if the sale is within the EU.
There is no grey area really, if you are in the EU and are buying it for personal, business or even pleasure (!), you have to pay the VAT. Business can of course reclaim the VAT from the purchase, private individuals can't.