When DD's teacher gives her different, more challenging work, DD tends to get very distracted and is more interested in looking at what the other cihldren are working on, rather than comleting her own work. She has always been a people-watcher, and even as a small toddler, she was always the last child to finish any activity, for example a library craft, because she would spend so much time watching the other children doing their work, before starting her own. It was never a problem until now. She is super slow at doing things like eating, getting dressed, getting ready to go out, using the bathroom, etc., because she is always thinking and talking about other things, rather than focusing on the task at hand. When we don't have a schedule, this is not a problem, but it gets very frustrating for the whole family when we have to be somewhere on time.
You are describing my DD4.5. She has always been an observer, and I have noticed as of late that this is causing her to be easily distractible. Our biggest problem is that it affects her socially. She is easily overwhelmed in large social settings by everything going on, and she is just not present. She is eavesdropping on the conversation over there, watching a boy be scolded over here, looking at how so-in-so is coloring a page, etc. Meanwhile, she has been repeatedly putting her arm in the wrong sleeve of her coat or ignoring a teacher's greeting.
I would say most four-year-olds are not being asked to focus for that long on work. I do not expect DD to focus when a lot of stuff is going on. I purposefully visit our art studio at slow times. If for whatever reason it is busy I quickly concede that we will spend the majority of our time there watching other kids. I think that is normal. I think it is too early to think attention issues. What you describe sounds above average for attention skills, and there should be a lot of development yet in that regard.