I wonder what those fungus lived on? This was in the era before fungus could metabolize cellulose. Maybe, unlike modern fungus, they just grew bit by bit? The fact that dead wood couldn't easily be digested is part of the reason the Earth's O2 level was so high back in the day, and why you could get coal or oil deposits even without anoxic conditions.

EDIT: All interesting information above from friends who know way more about the subject than me, who I told about the article. Any mistakes are probably mine.