There is a lot of confusion about the different species of morels (Morchella) that we have here in Ohio, and the fact that the mycologists keep re-classifying them every year doesn't help. See MushroomExpert.com's summary of the latest scientific opinions based on DNA analysis:
Black morels (Morchella augusticeps and related species) are clearly separate from yellow morels (Morchella esculenta), so if it was really a black in the video, it couldn't turn into a yellow without an act of God -- though it might have just changed its outward color due to sunlight, age, etc.
But the ones most hunters call "greys" actually are just young yellows (Morchella esculenta). Many hunters refuse to believe this, but they are genetically the same mushroom, and if you just leave a small grey grow it will mature into a nice big yellow -- unless it dries out or gets moldy. The same is true of the so-called "big foot" or "white," which is just a really big old yellow. That's the latest scientific view anyway, which is based on DNA analysis of the various mushrooms