The Living Force
For your consideration - rectangular and triangle-shaped clouds at different locations apparently photoed recently.
Starts at 6.28.
I don't wish to be dismissive, but i can't help to feel that videos like the one above are made in such a "spectacular" fashion that it (at least to me) gives me an opposite reaction. As if trying to squeeze out something that isn't there. And somehow, it doesn't really help, other than pouring more confusion to what may or may not indicate strangeness.
Personally I have seen cube shaped clouds on occasion, especially in autumn after cold air has swooped down the country and starts to stabilize; when the upper part of the cloud cover are limited by an inversion and the clouds can't expand in height any further. The Cu clouds can sometimes look "chopped off" on the upper side (as they typically already are on the lower side) - which together with the angle of illumination from the sun, make some cloud elements look cube shaped). So, in my book, it didn't look that odd, really. (albeit I can understand that in photos these can look more odd than to the naked eye).
Do you remember when we were kids and watched the clouds in the sky ? With all the lovely human imagination we've got, the childish entusiasm to point out things... oh, we could see so many things in the clouds...
I do not dismiss strangeness - but sometimes things are just made too spectacular in videos, reminding me a lot of annoying advertising on TV for a cheap "oh so great" products.