Please Explain Me !!

Hello, I would like you to explain one thing: in build 1 of 0.17, we could play offline only if we disconnected from the wifi, yes certainly, I thought this was a bug, more when launching build 2 (1.0), I can not anymore Enter Minecraft without being connected to the wifi, even disconnected from the account, and I even received a confirmation email wue this was not a bug, Now: EXPLAIN ME WHAT'S THIS!? Is this a check to see if the user is "original"? Please answer me, because I want to know.