No more arrogant than anyone else having a theory as to what the symbols mean. If you look again, I didn't say their beliefs were ancient, or that they claim it to be ancient knowledge. Not a lot is really known about ancient druids. Modern druids are reconstructionists. i.e. A lot of Druid groups do scholarly research, and then make up their own minds when trying to reconstruct the past, just like anybody else.

Probably why its called "celtic reconstructionism".

My comparison was in the idea that symbols can be giving topographical information, and not just symbolic or religious in nature.