It appears that at some point Activision had plans to bring the original Destiny to Steam, if SteamDB entries are any indication. This particular entry (now hidden from view) used to reference a ‘500 Destiny Silver’ microtransaction purchase. The original information can be seen in this tweet from the source.
The line about visiting Tess Everis in the Tower confirms this as being for the first Destiny (plus the fact that all the logo work is from the original game). Destiny 2 is bypassing Steam for its PC release in October. Instead, Activision have chosen to launch it through Blizzard’s Battle.net platform (which, as they’re now part of the same company, makes sense from that perspective).
That makes it pretty unlikely that the first Destiny is about to make an appearance on Steam. But it would appear to show that Activision played around with the idea. Whether a PC version ever made it beyond the conceptual stages, though, is not clear. There’s also always the possibility that it’s an elaborate fake entry.