I don't understand WTF Snopes is supposed to do about scenarios like this that seem to increasingly be the norm with call-it-like-I-see-em conservative news topics.
Blue Lives Matter posts an article of reasonable quality, it gets simultaneously hyped up and watered down (almost certainly on purpose) by other bogus news websites . These other websites get shared more by people on facebook, because for some reason fringe right wingers seem to have rather short fuses and low social media IQs. Snopes makes a sensible decision to go after rumors that either hit their radar first, or that appear to be the most popular source of rumors. Because of the insane pace that this stuff spreads, Snopes is always stuck playing catch-up, and as a result they are not going to have the time or resources to trace every single rumor back to their origins. As a commenter pointed out on the link you provided, the Snopes article doesn't even reference Blue Lives Matter.
If reliable conservative news sources (you said keep politics out of it, so I'm being extremely generous to BLM here) don't like Snopes picking on supposed strawmen arguments, they're going to need to start pulling double duty to nip this stuff in the bud before it spreads in the first place. They need to learn how to call out bullshit from their own allies, rather than waiting on douchey liberals to do it and then whine about how they didn't do it right.
Now that I've written this I already suspect it's completely pointless. If your friend sees minor failure by Snopes as a more serious problem than the idiotic game of telephone that's currently popular on right wing news websites, you'll have to completely realign his priorities to change his mind.