Interesting! Spoke to a German friend and he advised that it was probably pulled for being considered unsafe or too loud. Pretty much the same as what can be carried out in the UK too. The MOT is only a snapshot in time and if your car is subsequently considered unsafe or you're causing a nuisance you can still be prosecuted. I'd be interested to see if the post is updated with the exact legal reason why it was pulled.
Registering a car from the EU in another country can also be a pain - I seem to remember there was a good write up on BTG on the RX8. If it's standard it's less of a problem - if it's modified it can be very involved. If it's somewhere like Switzerland it's virtually impossible!