Hello! I don't generally add surface information unless it is something for me, so I have no idea on that. 

As for it being used for marching band, I guess you could say it is an assumption, but it looks exactly like the practice fields I'm used to seeing here in Texas. Example: https://www.openstreetmap.org/way/1324546234/history

Some are more elaborate than others, including football field markings and big circles (for some reason...).

The only other thing I think this could possible be is bus parking, but the lines seem to go in the wrong direction for that.

I am open to new information if you have local knowledge!