that is specially made and coded like that
lemme tell you how it's coded
1st slayertask easy : from lvl 1cb untill 30- (npcs rock crabs hill giants ,. . ..)
5 points or whatever it says
then 2nd slayertask is medium it will give you from you're lvl 30till 90 + 10 points or whatever for the same npcs because those npcs are coded in all off the slayer tasks except the hard one
so idk if u got my point but it's normal
specially made for that