Why do some guys act like this?

Like they'll pretend to flirt or do something for you but if you're not responsive, they immediately move to the next target right in front of you. For example, this guy wanted to give me some candy. I said no and he went to another girl and gave it to her.. And yes he likes her too. Another example, this guy called me when I was in the same room as him..probably just to disturb me. I looked over at him and mouthed what and indicated im not going to answer that and he can just walk a few steps to talk to me in person. Later on I see him busy dailing his phone and trying to call somebody else. Why do some guys do this? If anything its only going to turn me off because i feel like just one of his many interest.. Nothing special. Is it like they throw a net and hope they catch at least one kind of thing?