How come a company partners with Bitcoin?
I was checking out the Bitcoin website


There is no such thing. There are various communities and privately-run sites, but they are all distinct, and none are authoritative.


  I believe that Bitcoin is not a private company


That's correct.


  it's owned by its community


That's a matter of perspective. I would say it's not owned by anyone - not even any specific community.


  How is it possible for a company to partner with Bitcoin ?


They're not partnering with Bitcoin. They're partnering with bitcoin.com, a privately-owned and controversial website.