Would not think the less water part, but more like different soil parent materials from the native range up north, so maybe different minerals and heavy metals.no it is dry, actually darker in real life. it may be a hybrid since it's a landscape tree, sure seemed dark and well defined heart wood to me.
internet pictures look a lot lighter than this heartwood. possible due to dry air here, slower growth with lots less water?
My first thought was Oriental thuya, Pladycladus spp. Can't see enough to say based on your pictures. Did you have other pics when it was still standing?