No one knows how or what the Druids worshiped. There are Beavises and Butheads who, having watched Spinal Tap, assume they know everything there is to know about the Druids, but they are wrong.
Druidism is a reconstruction of the priesthood of the Celtic faith. And yes it is considered one of the religious that fall under the umbrella of Paganism.
Paganism is an Umbrella term. Many religions fall under this term including Druidism. It's like a baptist or catholic person saying they are christian.
Druidism is a Celtic Spirituality that focuses on Devin Nature, Spiritual connections, and Knowledge and Wisdom. it is a philosophy, a Religion and a Spirituality. yes it is Paganism, but a Druid can be any religion.
Druidism is a part of Paganism. Druidism is the religion of the Celts when the Church went to convert the British isles. Paganism is a blanket term used to describe all earth bound faiths that are not christian. A person can be Wicca, druid, or any other faith that honors the earth to be a pagan. A druid is the religious title of a person. The druids were the religious workers of the Celtic people,