This IS a lie. Do you have any sources?
There have been one attack on a gay couple, hugely used by the government and their supporting medias. Newspapers have implies (no facts) that the culprits where members of the strike against same sex marriage or far right activists. There was then a huge huge buzz to shame the strikers. And finally, 4 months later, the police arrested 4 youths: 3 in a "cité" (public housing, "ghetto") and one was already in jail, all of them well known of the police services for violence facts. http://www.leparisien.fr/paris-75/agression-homophobe-a-pari...
Some people in the comments do say that the police delayed the arrest so that the government could shame the protesters against same sex marriage.
One more thing, the man beaten reacts to the arrest on a far left web site. https://bellaciao.org/fr/spip.php?article137205 And he is in a complete deny, not being able to recognize that those who beat him have nothing in common with those that protested against same sex marriage.