Face ID Issue

I recently purchased iPhone X because I wanted a higher degree of privacy (as boasted by Apple). Like others, I also set ip my face ID. Recently, my brother (even we’re not identical twins) tried to unlock my iPhone using his face (even his face ID wasn’t set up), and, to my horror, it worked. Woe to Apple!

Apple always talk about privacy, security but of no use. What’s my fault? Is it that I bought this costly phone just to compromise on my privacy?

After I set up my face ID, whenever he (my brother) tries to open it using face unlock, it works.

I would boast about having an iPhone X, but I lament now! Sigh!

I need your support in this regard! I hope you’d help me!