best to keep schtum, and if and when your friend realises there are similarities, point out you had spotted it but prefer their version. That should do it!

But there may be some heckler who spills the beans and doesn't have the ettiquette!
I wrote a song delineating the Victorian trade of Pure Finding (collecting dog poo to sell to the leather trade) which given the subject is (had to be) humorous. And I have had comments that someone (Stanley Accrington?) had already written the definitive dog poo song. His was about "People keep emptying their dogs down our street". People make the most tenuous comparisons and think you can't visit the fringes of a territory without being second or inferior. Or write a humorous song about a genuine Folk/Historical subject. Like there is only one box to tick! Only one circle in a Venn Diagram! People? What are they like?