What does 相逢是首歌 mean? Google translate:
"Meet is the song"

But that doesn't make sense in English, could somebody try to come up with a better translation?

I see 相逢 probably means "come across" here
and 首歌 is really unclear what it means "first song?"

I want to say it means "I came across a song"

But it's just really unclear to me

It's from this song: https://www.youtube.com/watch?v=OeuHZjz1FZY
It does not make sense in Chinese either when it is without any context.

After reading the lyrics, it just means "(Our) meeting is like a song". And "you and me are the singers of the song". It is metaphor.