Can anyone tell me if this is mold or mildew?

This is the floor of my tent. I put away after my first backpacking trip and we didn’t experience any rain or anything. I took it out to clean it off four days later and noticed this. Very hard to see with the naked eye but it shows up when held up to the light. Sporadic dark spots. I’m hoping to get some help identifying it so I know how to clean it. I’ve already tried scrubbing with white vinegar mix. Thank you in advance.