I don't know if there is a norm here, Dubi should know better but Tsur is an honest guy and note that he said that kamada is not for sail but he did not denied any other relations or cooperation.
The norm in Israel is to deny false rumours as well as true rumours.
TEVA is probably the only company to adapt the US business practice of denying false rumours and not commenting on true rumours.
2 recent examples of Israeli companies traded in the US only, TERN and FLSH denied rumours of their sale negotiations for months. Needless to say the buyouts went through.