We actually had a quick adjustment when we launched and immediately changed the name of the instance after the Pixelfed dev contacted us about the domain. You can see the pinned comment here: https://lemmy.ca/post/39411782

As for why both instances exist

We both launched around the same time. I think this is their launch post, which had it about a month before we launched https://cosocial.ca/@mwdawson/113839618312626769 By the time I learned about that instance, we already set up pixelfed.ca and were preparing to launch

I think there’s an advantage to having more choices available to users. Also lemmy instance admins often help each other out, and I’m sure it’ll be the same with pixelfed :)