He said: 'It's what happens, it's football. It is what it is. It's just what happens, it's football and stuff happens. It was one of them things I suppose.'
Lopes later retorted: 'I don't think it's part of the English atmosphere to hit an away player but it was like that.'
Lyon forward Bertrand Traore was shown a yellow card after confronting the fan who struck his team-mate.
Traore told L'Equipe: 'In these heated moments, like the fight, we have to help each other, stay as a team. That's what I tried to do. There's a supporter who puts a blow to Anthony Lopes, I think it's not normal. I defended him.'
The incident occurred midway through the second half when the score was 1-0 to the visitors.
Williams later equalised for Everton, only for Traore to restore the Lyon lead which had earlier been established by Nabil Fekir.
Everton have now taken just one point from their first three group games in the Europa League this season.
The defeat - Everton's sixth in their last 10 games in all competitions - piled more pressure on manager Ronald Koeman, who criticised the standard of officiating.
He said: 'There was a certain irritation in that moment by Ashley because he's that player who likes to win and who cannot deal with a lot of disappointments.
'But I think the mistake was also by the referee because they make a lot of theatre and he did nothing.
'Fekir was I think 10 times on the floor diving [and] not even a yellow card. And that grows our irritation and even extra time... It's five minutes. We had six substitutes and that's three minutes.
'We had the fight and that was maybe two minutes and they had I think eight times injuries in the game and it's five minutes... come on, please.'
Speaking on BT Sport, pundit Jermaine Jenas suggested that Williams' meltdown was perhaps the result of the defender struggling to deal with what has been a hard period in his career.
Jenas said: 'The last couple of weeks will probably go down as the toughest weeks of his career.
'Getting knocked out (of the World Cup) by Wales in the way that they did, a lot of that fell on his shoulders in terms of the way they went out.
'(He is) captain tonight and the pressure that Everton are going through, it seemed to me like that all came together and he lost control in one specific moment.'
Lyon expressed their disapproval at Williams via their English language Twitter account, posting a photo of the Welshman throwing a punch at Tousart along with the caption: 'Is this football ?'