Until Xur starting selling shards again (this week) you could only get shards by breaking down exotics. The 2 for 1 method is a way of getting a shard for 2500 glimmer and a few Motes instead of breaking down valuable exotics.
As far as the method being documented, I’ve done it about a dozen times. It works. Heavy weapons are best, because they take the fewest Motes (6-7) as opposed to specials (13-14) or primary (20-21).
