Listening to the song, Happy Man played live has made one of my friends think that it has been inspired by another one. Later to my question it turned out, he was thinking of 'Naive Song', performed by Mirwais, a French musician, as far as I know.
I listened then to both of them, found little similarities in the tune and rhythm, a little bit more perhaps in their feel, their being rather melancholic (despite the tunes). However, I am still not convinced, that my friend's feeling is right, as I also see similarities, say, between Naive Song and Pulse. As thinking about this issue will not take me closer to the answer, I thought it a good idea, to ask whomever is concerned
Thank you in anticipation of the anwer,
Éva