Created attachment 187745 [details] Filelight, as well as [df -h] show way lesser disk usage than dolphin Dolphin is misreporting Used disk space.
Your screenshot shows that both df -h and Dolphin agree on the available space as well as the total space. Dolphin calculates used by subtracting the available space from the total space, while df -h looks at the actual data I believe. Dolphin is not inaccurate because the "used" space includes data, metadata and the reserved space.