You are operating under a Sola Scriptura protestant doctrine. I do not. I never said it was ok to use Easter, it didn’t say it was incorrect. The Word Easter is an old English word that they used for Easter.
As I said, in Latin-Roman Catholicism, the word is Pascha/Pasqua in Italian, the French and Spanish have similar words that are derived from Latin.
And yes the celebration is indeed Christian, Church Fathers who were pupils of the Apostles celebrated the feast (Polycarp, for example, a pupil of the Apostle Saint John).