Former Lancaster CA resident here.
I don't know anything more about this story either. But it sounds highly atypical. Lancaster doesn't have its own police force, and contracts with the Los Angeles Sheriff's Dept. for coverage. As a general rule they're lighter-handed than the average metro cop shop, possibly because they're spread thinner and don't have time to pursue bullshit.
But a few years ago, when the Feds told L.A. County that they'd have to reduce their jail population -- they picked out the problem prisoners and dumped 'em wholesale in the Antelope Valley. What had been isolated perps sneaking around in the dark suddenly became swarms of perps boldly going in broad daylight. Theft abruptly grew from the usual petty urban stuff to a cottage industry (particularly for metal), and same for gangs and drugs.
So I'm thinking this might have been a sting against a large drug or metal-fencing operation, using the cellphone thing as cover for what they were really after, not to mention as a quick way to ID both those present and those who needed pursuing.
Not justifying their action (which was, IMO, blatantly unconstitutional), just thinking of rationale based on the local situation.