Their car was not entirely on their own property, it was blocking the public right of way.
https://abcnews.go.com/US/video/sf-couple-fined-1500-parking...
I don't know where their property line is precisely, but it simply isn't true that they're blocking the sidewalk. The back of their car is well clear of the sidewalk. It's not even close.
https://i.imgur.com/87lHdux.jpg
https://i.imgur.com/4Ls9Upx.jpg
Furthermore, the city is waiving the fine if they build a roof over it. Would that make any sense if they were parking on the sidewalk? Building a roof over the sidewalk so they can continue to park on it? Obviously they're not on the sidewalk.