L.R.
Your daughter's way too young for big labels like "introvert" to get stuck to her. How the teacher perceives her (and how the teacher then treats her, based on that perception and label) are all affected by the labels she's given at school. She's not even in kindergarten yet.
It's not clear to me what the teacher means by "she just plays with the children who are around her" at school. Does that mean she plays with kids who sit closest to her, who are in the closest physical proximity in her class? Or does it mean she sticks only to kids she she already knows from outside school? Either way, it makes sense: She's only four, and will go with what's familiar and/or most convenient. Not a lot of four-year-olds are socially ready to cross the whole room and ask a kid they don't know well, "Want to play?" Some are, but not all, and that's OK.
Does she actively resist when she has to interact (in a game or other class-wide activity) with certain children? That would be more of an issue. Find out in much more detail what the teacher has observed -- get specific examples. It might even be that your daughter just doesn't click with certain children in the class and prefers her free play time to be with other kids with whom she feels more comfortable. That's normal, to me. She's also at an age when having "best friends" starts to be important, so you might hear her talk mostly about a handful of kids she is really into right now -- the "several children who are around her that she often mentioned" as you put it. That list of kids will change eventually.
But in the meantime, other than keeping good communications open with the teacher and being sure your daughter stays active and has play dates at home with a variety of kids she plays well with -- other than those things I wouldn't worry about it, unless it becomes some issue of her resisting doing what the class as a whole is asked to do. If she's at the point of not speaking when spoken to, or really being withdrawn, that would be a problem, but from what you say about her home behavior, that doesn't seem to be the case at all.