Well, yes, that's true, and I'm not, of course, suggesting that Christians were the first to decorate eggs. However, the association of eggs with rebirth, resurrection and hence the link with Easter, and its incorporation into popular Western culture as The Easter Egg is (or was originally) a Christian phenomenon.
As an aside, there's nothing particularly wrong with borrowing (or appropriating as the woke would call it) aspects of cultural practices from other societies. It would be a very boring old world if we were all restricted to our own native cultures only.
When it comes to religion, there's nothing new under the sun. New religions borrow from older ones; old religions borrowed liberally from pagan customs and secular society borrows from religion and vice versa. Nothing wrong with any of that, of course, but the problem arises when there is a concerted State (or EU) attempt to suppress a particular form of religious tradition.