I was under the impression that the forums here were changed so that a ‘guest’ user couldn’t post – i.e. they had to be registered and log in with their preferred username. This seems not to be the case.
Perhaps we should think about changing it – not because it would be excluding potential posters, but because if one can post without registering, then it opens up the possibility of spam posting. Something I’ve yet to see here, thankfully. 
– Thomas Adam