To clarify and clear it up a bit:
Say, you have 1 account named xxa, and your brother have another account named xxb. At one time with 1 PC, you can login with your account(xxa), and then, after you finished playing (and therefore logout your account from the PC), your brother can also login with his account(xxb).
The Q&A actual intent was that you cannot login with your account at the same time as your brother login with his account in one PC - therefore, no multi-client in one PC at a time.
Sorry if my translation didn’t deliver the Q&A original intention clearly! I’ll try my best to translate other stuff better next time!