Because the EUMC definition says could in the context in which it is said - not simply "could" like it could be raining. Because if it is actually raining outside then it "is" raining not "could" be raining - see the difference. The context in which Flynn defamed Mr Gould was antisemitic since he questioned his loyalty solely because he was a Jew who considered himself a Zionist (as Churchill declared he was) with doubtful roots to Britain and based on no other evidence than that.