This is my first MacBook but Apple Music showed three authorized computers???

Today, I checked my Account Settings and saw that there were "3 computers are authorized to play content purchased with this this Apple ID?" -- I wonder why did this happen? This is my first MacBook. Where is the other two computers?

To be safe than sorry, I have deauthorized all computers. However, I still wonder why there were 3 computers that were authorized? Also, I checked under "Manage Devices", all of them were iPhones (I've owned quite a few iPhones, but no MacBook in the past), where did the other two computers came from? Did anyone have the same issue with me? Thanks!