Don't dwell on this problem. This question is related to the previous education syllabus. Coulomb's law applies not only to vacuum, but also to medium. Before this, it is necessary to explain in detail that Coulomb's law is applicable to the case where the field source charge is stationary and the force charge is moving, but it is not applicable to the force of the moving charge on the static charge. But the point charge is an idealized model after all, and it was later changed. Your question is correct, but now you just need to remember vacuum and electrostatic charge. After all, Coulomb's law has limitations.