... the wealthy San Francisco suburb of Orinda ...

Do article authors Stefanie Dazio and Daisy Nguyen live anywhere near the SF Bay Area?

Orinda is tony, but between Orinda and SF are the rather large city of Oakland and San Francisco Bay!

Orinda is about 15 miles ENE, straight line, from SF and a similar distance south of Vallejo.

I could understand some NY reporter not thinking to look at a map and making this mistake, but a supposed Bay Area reporter?
Orinda is in the hills between Oakland and Walnut Creek, with three reservoirs near the town (lots of recreation opportunities). "Wealthy" might be a bit of an over-statement.
Vallejo being as far from Orinda as it is, and even farther by car, I'm going to speculate that the killer was either part of the party or had followed the partiers to Orinda. Vallejo has become a bit of a rough city since the closing of Mare Island. There have also been a number of shootings on I-80 between Vallejo and Berserkeley.