Riddle: why is the parameter UIView in one place and UITapGestureRecognizer in another?

gistfile1.m

#import "UIView+DTActionHandlers.h"

#import <objc/runtime.h>

char * const kDTActionHandlerTapBlockKey = "DTActionHandlerTapBlockKey";
char * const kDTActionHandlerTapGestureKey = "DTActionHandlerTapGestureKey";
char * const kDTActionHandlerLongPressBlockKey = "DTActionHandlerLongPressBlockKey";
char * const kDTActionHandlerLongPressGestureKey = "DTActionHandlerLongPressGestureKey";

@implementation UIView (DTActionHandlers)

- (void)setTapActionWithBlock:(void (^)(void))block
{
	UITapGestureRecognizer *gesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(___DTHandleTapAction:)];
		[self addGestureRecognizer:gesture];
		objc_setAssociatedObject(self, kDTActionHandlerTapGestureKey, gesture, OBJC_ASSOCIATION_RETAIN);
		
		// dynamically add the handler method
		void(^handler)(UIView *) = ^(UIView *sender) {
			UIGestureRecognizer *gesture = objc_getAssociatedObject(sender, kDTActionHandlerTapGestureKey);
			
			if (gesture.state == UIGestureRecognizerStateRecognized)
			{
				void(^action)(void) = objc_getAssociatedObject(sender, kDTActionHandlerTapBlockKey);
				
				if (action)
				{
					action();
				}
			}
		};
		
		IMP myIMP = imp_implementationWithBlock((__bridge void *)handler);
		SEL selector = NSSelectorFromString(@"___DTHandleTapAction:");
		
		class_addMethod([self class], selector, myIMP, "v@:");
	
	objc_setAssociatedObject(self, kDTActionHandlerTapBlockKey, block, OBJC_ASSOCIATION_COPY);
}

- (void)___DTHandleTapAction:(UITapGestureRecognizer *)gesture
{
	if (gesture.state == UIGestureRecognizerStateRecognized)
	{
		void(^action)(void) = objc_getAssociatedObject(gesture, kDTActionHandlerTapBlockKey);
		
		if (action)
		{
			action();
		}
	}
}

I found through testing that if I add the method dynamically then the gesture recognizer passes the view to it where it is attached. The normal behavior is to get a pointer to the recognizer itself as parameter. Why is that?