To be honest with you, not all songs have a meaning or a reason to be. This is one of them: it was probably (along with "Laura") one of the first songs I wrote on 7-string bass. So basically I was playing around trying to get used to my new instrument and then I started experimenting with the capo and this tune appeared, it kind of "made sense".
I love when the process flows this way, kind of "unconsciously". You know what needs to come after the first part and by the time you realize the song is done. It sounded quite "uplifting" to me so I called it "This must/could be happiness". It's a bit of the same thing in real life: sometimes you're not sure if what you are feeling is true or not.
So the fact that you wrote the song unconsciously probably means that there is an unconscious reason for it. But at the moment I don't know what it is, so it will probably come up in years to come.
There's also another good thing about songs not having a meaning: it won't change the meaning it has for the listener. Sometimes you listen to a song and it means something to you, but then you find out it's actually about something completely different, so it can be a bit of a disappointment. It's interesting to see what this song means to different people: some people see the beach, some others a motorbike ride, some get a spanish/flamenco feel.
And all of them are absolutely valid. In the end, once any piece of "art" goes public, it kind of has a life of its own. It's some kind of a child: it's got some of your traits, but it's completely independent.
While I was doing my internships in a recording studio back in the day, I had the chance to work with one of the most talented musicians I've met: Pedro Andrea. He was recording a song and then he said: "You see? Music is the f*cking time machine. I wrote this song some years ago, and as I play it again it takes me back to those days, I'm feeling now what I was feeling then".
So in the end I guess is not that important what the song means to you (as an author). Maybe your song reminds somebody of a person, or a place, or a time. Who are you to take that away from them?