I don't think it is whataboutism in general. (It probably is if it's specifically targeting the HN thread, but that's now how I read it.) It's not just waving at someone else's misbehavior, it's noting that a double standard (examine bias in case A, acknowledge but ignore it in case B) is producing an agenda.
In mainstream discussions, there's a pattern of discussing WL bias against a baseline of whatever American mass media says. To repurpose a point from up-thread, that creates a situation where "how biased is WL?" is both a legitimate question and a misleading distraction.
If you want to create an informative media diet, you might ask "how biased is each source, in which direction?" You won't find objective truth, but asking that at least lets you curate inputs so that you won't have important information from any side go completely unmentioned. Lots of people I know do this, adding up equations like "NYT and Intercept both skew left, but one is largely pro-government and one anti-. BBC is moderately pro-government, but since it's a different government it reports US news better." Asking about Wikileaks is vital in that context.
If you want to distract from unpleasant facts, you might ask "How biased is Wikileaks in the direction of Russia?" And then the answer is treated as inherent bad - the more biased, the less attention should be paid. "All news is biased" is defeatism, but "all news is biased, how biased is Wikileaks?" is still manipulative because it ignores the magnitude of non-WL bias. I see that trick used a lot when US politicians and reporters cover Wikileaks, and it smuggles in an that we don't need to seek balance, just exclude a few too-biased voices.