I have been told that if someone does not perform Salaat he becomes a kaafir even if he believes Salaat is Fardh.

Answer

Perhaps you did not understand what you were told. Nowadays, modernist Zindeeqs although they come to the Musjid on Fridays and also attend the Musjid irregularly, they do not believe in the fundamental institutions of Islam. The abstention from Salaat of such zindeeqs is undoubtedly kufr. But, abstaining from Salaat whilst believing that Salaat is Fardh is not kufr. It is a terrible sin which threatens to eliminate Imaan if the sinner perpetuates his evil practice of abstaining from Salaat. But it is not kufr although it can ultimately culminate in kufr.