I've seen this happen before in other areas, and honestly, I think it's this blog just making a huge mountain out of a molehill. The weapon names could just be (and probably are) placeholders and the "ep3" could mean
anything, given the context. Bungie made
references to pirated betas of Windows NT and Mac OS in
Marathon; does that mean that they used confidential pre-release Microsoft and Apple OS code in a first person shooter? Of course not.
I'm not ruling out code-sharing, of course, between DOTA and the Source engine. But you're likely to find real hard evidence of that in the actual code itself, not in file path names.
Until there's anything to show me otherwise, I'm going to take the jaded approach to this and say that the blog's owners and writers shrewdly wrote an overly sensational hack piece for the purpose of link-baiting to either get publicity or revenue from web traffic. And it seems to be working.