They went on to: "Reports that NSA or any other part of the government were aware of the so-called Heartbleed vulnerability before April 2014 are wrong." so there's no weasel-wording going on here.
Perhaps they're using the etymological root of aware, which is "wary", and they mean they were unconcerned with its existence as they were unwary/unaware of any possible dangers with it since it was unknown to hostile forces.
That could mean anything from "there was a typo" to "there were factual omissions that were unknown to the author".