It is entirely possible that the Russians were behind some or all of the hacks. However, we don't have sufficient evidence to prove that. For one, Cloudstrike

It is entirely possible that the Russians were behind some or all of the hacks. However, we don't have sufficient evidence to prove that. For one, Cloudstrike was referring to DC Leaks, not Guccifer 2.0 (nor Wikileaks). Further, it is very, very rare for intelligence services to release private documents to affect an election in another country. It is far more common to use that intelligence to affect diplomatic relations between leaders (i.e. to get policy outcomes), not to affect the populace of a country. Finally, I'd argue that just because the Russians hacked into one or more servers does not mean that an American didn't leak the documents. It is possible (though I will admit less likely) that both occurred: the Russians hacked the DCCC, but a lone FBI agent leaked documents to e.g. Wikileaks.