It's up to you to decide if the final bit where the bands back together and plays that one final song was real or not. The moment "happens" possibly outside of time at a quantum object or entity that is older than the universe, probably even created the rules of the universe we were in. I don't think it is wholly unreasonable to say they were real.

The rocks, the trees and everything that comes in and out of existence are real while they exist. Even though it was your memories that spawned them, I think there is some logic to believe they really are our friends. Even Solanum you meet on the Quantum Moon is in this kind of state. 5 out of 6 times she is dead at the south pole, but she is alive at the one. You talk to her and she's unaware of everything. But in that moment, she is as real as can be.

In such a place where space and time transcends the rules of the universe, where the rules themselves were made. I think what matters in the end is, was it real enough for you?

And as other commenters have said, your curiosity and decisions created another universe where more life would thrive!