As salamu alaykum sister,
Your concerns are common. Often times as children develop they can take on the interests and mannerism of the environment and people which they are around. In your son’s case, he was surrounded by girls most of the time.
One the other side, often little girls play with boy’s toys, climb tree’s, prefer boys clothes, and for lack of a better term-they are “tomboys”! They usually out grow it after a few years as I suspect your son will. The less you mention it, or ask him about it, the sooner it may dissipate. Often times when we put a great emphasis on something we don’t prefer, it makes the child go harder towards that behavior or goal. As long as it is not haram behavior, I would try re-socializing him by having play dates with other boys, have his dad, grandfathers or uncles spend more time with him. You may be able to generally recondition his tendencies by having male friends and family take an interest in him and do things with him that he finds enjoyable. Also insha’Allah, enroll him in boys groups and classes at an Islamic Center or your local Masjid so he can develop new interests and make lasting friendships with other boys his age. And don’t worry too much, this phase will insha’Allah pass soon enough!