Crime is probably the best hypothesis but the other one to consider is that they have some sort of minimalist aesthetic, and they genuinely like the look of grocery bags (and nondescript bags in general).

If this was a security through obscurity tactic, why would they publish this blog post?

Yes! https://news.ycombinator.com/item?id=45338980

You think laptop thieves will read the blog and start stealing brown paper bags on the off chance there's a laptop inside?

To me it seems like a pretty good strategy, with the downsides being you have to lug it around by the handle (no back or shoulder strap, which would spoil the camo effect), and it doesn't have pockets for small things like cables / dongles / etc.