That was also my immediate thought. However, what was the chance that the method they did use would end up not working? If sufficiently low, from an EV perspective, perhaps they made the right choice? Also the article isn't clear to what extent the lean is responsible for the building not being finished.
That helps with storage, but still is larger than a bigint, and doesn't help with the random distribution of data. I believe newer versions of MySQL have a data type for this.
I think this can also be problematic. Long lived code _must_ work, which is good. However, it can also live a long time for bad reasons. I have seen long lived code that only lives a long time because it is so complicated that no one can understand how it works, or written in a way that is very hard to change. So it lives a long time, because no one wants to take the time or effort to touch it. Finally, when it _must_ be changed to support a new feature, it might require a full rewrite.