Yes, children, this is what will happen if you don’t take care to control your mint.
Experienced gardeners are always warning novices about this. Mint is a perennial that does very well in this area and quickly spreads underground. The community garden mint varieties are grown in big tubs that contain the roots. This patch has no such barriers, and advantage is obviously being taken.
I have a feeling this plot has been abandoned. Best of luck to the person who inherits it next year. I hope you like mint tea.