Destiny 1 Silver becoming available on Steam of all places was in fact put there by Bungie.
After everyone started theorycrafting following yesterday's news, it now appears that this was no elaborate hoax by a third party.
David 'DeeJ' Dague, community manager for Bungie, confirmed that Silver was actually made available on Steam in error, and that all purchases will be refunded by Valve.
When one Twitter follower rightly asked, "How do you sell microtransactions for a game that literally doesn't exist on PC?" DeeJ didn't give a satisfying answer. "Spoiler: You don't," he said.
In a separate tweet, the veteran community manager reiterated that there are no plans to release Destiny 2 anywhere but on Blizzard's Battle.net app. Although this statement may have shut down speculation about Destiny 2 coming to Steam, it only serves to raise more question about Destiny 1.
The question was never whether or not Destiny 2 is coming to Steam, since the Silver listings on the Steam database clearly referenced the first game. Not outright denying a PC version of the first Destiny is in the works may also carry a meaning.
A possible scenario here is that Bungie was testing the system ahead of a future launch of Destiny 1 on PC. The game is now content complete, and a game of the year-style version on Steam would make a lot of sense. This could possibly also be for a free-to-play spin-off supported by Silver microtransactions.
Time will tell. For now, PC players have the upcoming Destiny 2 beta to look forward to.