It was an annoyingly stupid article. Just speculates that the leak 'must' have been from a 'liberal' and then woffles on from there.
See, it 'must' have been a liberal, because it's liberal judges who are 'activists' - ignore Thomas being married to someone who urged the overturning of an election result, that isn't "activism". Nor is mounting a multi-decade effort to specifically take control of the Supreme Court at all costs, in order to achieve your political goals. That's not 'activism' either, apparently. Only liberals can be activists.
He also illustrates the 'politicisation' of the court with a list that puts the Merick Garland gaming of the system on a par with some Dems merely _talking_ about court packing (which is clearly a _response_ to the politicisation, not a cause), and not even mentioning Barrett's rushed confirmation. Really passive-aggressive sneaky bit of spin, there.
And of course he ignores the _content_ of the leak, as if the leak itself is the 'real issue' here. Probably is slightly more likely it was leaked by someone on 'team liberal', but the politics of the leaker is surely a secondary issue? It's not impossible the leak might not have been political at all, either way - just someone in a junior position over-excited at having a bit of extremely-high-news-value inside information.