In France 1 April is known as Poisson d’Avril. Children stick paper fish on to the backs of as many adults as possible. They then run away yelling Poisson d’Avril. I guess this cyclist is a teacher or otherwise knows a lot of kids.
I think it’s also why the chocolate shops are full of chocolate fish. Well, I guess it would be rude not try some.
Thrown to (the) Lyon 