Good point. Those same requirements also state that you need 8.8 GB of available storage to install.
Technically, both the RAM and storage requirements are true. Sierra will install and run with 2 GB RAM and 8.8 GB storage, but it will be a horrible experience. The machine will run horribly slow. Then, in a few minutes when you run out of free disk space, it will grind to a halt. From other reports here on Apple Support Communities from people who have run out of disk space, recovery may not even be possible. You would have to erase your hard drive at a minimum. You would not be able to restore from backup because that would fill up your hard drive again.
For the best Sierra experience, I recommend 8 GB RAM and an SSD.