An extremely valid question which deserved a simple answer.
How was Gerry supposed to answer that question without giving the impression he was well-acquainted with Murat?
http://www.mccannpjfiles.co.uk/PJ/STEPHEN-CARPENTER.htm (rogatory)
*snipped*
Then a voice called me from over the hedge. "What is happening, or what is going on'", I replied that a three year old girl had disappeared, he said "I am going to come round to talk to you" and he did this, walked round to come over towards me and said "I have lived here for fourteen years, I speak Portuguese fluently and I can help to translate", and we introduced ourselves, he told me he was Robert and this was the first time I had seen this man. Robert mentioned that he had a daughter in Norfolk who was the same age as Madeleine, and that is why he was able to understand what they were going through. We walked back along the path that I had taken to Gerry's apartment and I explained that Robert spoke Portuguese fluently, he told Gerry that it was important to have someone who spoke the language so that nothing would be lost in translation.. And that was how Robert Murat was presented as a translator.
DCF: Yes
SC: After he left, he explained that Gerry was frustrated with the way in which the case was being handled and they went to talk to John Hill.
We can only speculate what information Gerry imparted to Murat but it is clear the two men had met prior to the media's question. That's not quite the same as "knowing" someone in the sense of a friendship.