Yeah, That's A Worry.

https://www.youtube.com/watch?v=aaQetOuCJf8&pp (Alibi, Ella Henderson Ft. Rudimental, Official Visualizer).

Apparently when Ella Henderson was first offered it, she thought it was an original song.

https://www.youtube.com/watch?v=Tw0_qHNRAEA&pp (Gangsta's Paradise, Coolio, Official Audio).

Knowing nothing of the battle to get the sample cleared for the song Rudimental were sampling.

https://www.youtube.com/watch?v=1TLFnokO1Oo (Pastime Paradise, Stevie Wonder, Songs, Official Audio).

Obviously I can't speak for every Eurovision entry there has ever been, or will ever be.

However, customarily speaking It's not an attempt to pass someone else's work off as your own.

It's a way to acknowledge someone else's work.

Of course. 

There's a reason why I was doing that in the night of Simchat Torah.

https://www.youtube.com/watch?v=7BmjVI712IE&pp (Bittersweet Goodbye, Issey Cross, Official Visualizer).