I found all my emails into my brother's icloud settings

6 months ago I was surprised when my brother could connect to my wireless network without giving him the wifi password.

We live in two completely different cities and I just moved to that house recently. I didn’t stop at this even though I kept thinking about it the whole time.

Today when I was fixing something with his contacts sync, I found all my emails, business emails in his [Settings -> internet accounts]

We have two completely different iCloud accounts, how could that be possible?