Non-photosynthetic plants (like ghost pipes) are typically rather small parasites of other plants, that for some reason lost access to good sunlight (such as being so deep in a forest that other plants call dibs on those yummy photons). I don’t see how it would be the case here, given the fossil in question is 8m tall, and apparently it predates actual (Viridiplantae) trees. And I think the same reasoning applies to a potential Rhodophyta = red alga.

In fact the size is bugging me. Why did it grow so big? Plants usually do this because they’re trying to outcompete other plants, but the Wikipedia article about the taxon suggests it was heterotrophic.