Which is exactly the point, anyone expressing surprise at their behaviour has not followed their reputation for many years now.
Lazio have always been a nasty racist / fascist club.
I have colleagues who live in Rome and they wouldn’t be seen dead at a Rome derby and they are staunch Roma...
To be fair, lazio has always been known as a fascist team...remember the show of fury from the football world when the Italian footballer/ manager Paulo do canio joined and was pictured doing a Nazi salute.