Another recommendation when dealing with contractors who don't speak English very well... Use very simple sentence structure and vocabulary. "It is quite possible you misunderstood my reasons for clarification" is pretty tough vocab for a non-native speaker..
Simpler is: "I think you did not understand me."
I learned this (the hard way) when I did a lot of work with Japanese game companies. It may sound very harsh and abrupt to our ears, but it is far less likely to be mis-understood.
And, yes, unless it is crystal clear that you're asking for a 'demo' (which has been pointed out is not without some controversy), it could easily cause some hard feelings.
That all said, the advice from frob, etc is spot-on. Best to just let this go and let it die down