The guy in the video kinda struck me as - I'm trying to say this in a nice way - prejudice to his understanding of mold/mildew - not open minded. Why was he so obsessed with the stain? With just a little bit of research, I learned a few useful tips.
Mold/mildew can take hold within a couple days, and must be dealt with immediately. Yeah, in the video, he completely forgot about it (no fix for that), but in wet, warm weather, open your tent as soon as possible when you get home or stop for the night. Don't wait for dry weather. It's the closed up and not open to fresh air environment that mold/mildew thrives in. "Moisture from condensation, humidity, rain and snow can leave your tent damp after an outing. Even small amounts of moisture can leave your tent vulnerable to mold and mildew growth." I would recommend opening and airing out your tent after every use, no matter what the weather you experienced on the trip was like.
Current technology has shown that tent material needs to breath. That's why it's not totally waterproof and yet it's the fabric's downfall for mold/mildew damage when neglected. The mold/mildew can get a foothold in the pores of the tent fabric resulting in stains that can't be removed with out almost destroying the fabric. Mold and mildew stains are difficult to remove. If the area does not smell like mildew, the mold has been destroyed and the stain is just a visual but harmless mark.
It may not be a good idea to use bleach, to clean the mold/mildew off your tent. Bleach is corrosive and can damage the fabric and weatherproofing. An alternate treatment is a solution of one quart of vinegar and a half a teaspoon of dish soap in 5 quarts of hot water. I'd recommend checking with manufacturer's website or help desk to find out what their method of treatment is before cleaning. On canvas, it's recommended to use hydrogen peroxide.
Some useful sources:
Treatment
How to clean Mildew