Prostitution in Belgium is legal but certain related activities such as soliciting and pimping are illegal.[1][2] Belgian municipalities may also introduce further prohibition or regulation.[2]Human trafficking or exploiting individuals involved in prostitution is punishable by a maximum prison sentence of 30 years.[3]
I think what he was getting at is that the dutch would be offended at Belgians being called "first to decriminalize". Though i think this technically true, there are however a number of other countries in europe where it is legalized including Netherlands, Germany and Gwitzerland if I recall. It is fully legal, recognized as a legit profession / occupation and regulated. I think decriminalization is simply making it not illegal.