Skynet is here xD

Oh, man, look at that! That robot plays exactly like someone from [that sports team you don't like]! So uncanny!

Squenix didn't actually do anything wrong* (this time), it's all on how Valve has store page data configured.

See, the base game is no longer available for sale, so Squenix changed the title of the store page (which only has the complete Definitive Edition bundle version of the game on it) to properly reflect what content is being sold. However, Steam info calls only pull top-level data from a page (which is also why during sales both Steam store searches and API calls will mess up price data for certain listings, as lowest current pricing [regardless of associated max price] will always top-level on the page), which means that any game associated with that store page is going to come up as "Definitive Edition".

Of course, you could say it's SqEnix's fault for not just posting up a new store page, similar to how State of Decay and State of Decay: YOSE are seperated, but that's also not typical practice for Steam store pages unless the versions of the games are different (as is the case for YOSE, which is a rearranged version of SoD+DLCs, rather than just being SoD+DLCs alone).

Anyway, tl;dr version, API calls to the APPID associated with the base game are pulling up the title and pricing of the Definitive Edition due to how Steam has things set up, and because SG staff doesn't typically manually edit associations**. On the page itself, SqEnix does have everything properly presented.

* (Unless, of course, you consider them never including DLCs into bundled Tomb Raider base games, even though base games are only bundled after base games have been removed from sale, "wrong". It's certainly an unusual practice, in any case, so we can at least say they have some small degree of responsibility, since it should be clear on their end that Steam's presentation will make it so the game may be misassociated as being a complete edition.)

** (And in this case, the actual Definitive Edition is listed as a Bundle, which can't be referenced by API calls, so they're actually limited in what they can do to begin with. Best they could really do is change it so that the title is overwritten to remove the "Definitive Edition" part, while still leaving the rest of the association as-is, since they still need to have it so that the Definitive Ediiton can be referenced [due to store keys] and they can't really do a double-reference to the same APPID. There may theoretically be some workarounds they could do (like associating to the actual ID of the store keys and manually reassociating it to the APPID of the base game), but let's just assume that the whole thing is a hassle, even if possible.)

Aaw man, hope you can get that sorted out! :/

Then go through PayPal and add there your CC and then subscribe with it to the Humble Bundle Classic Plan. I have read a lot of people working that way around Humble Bundles "Your CC is not accepted" issues on a regular base.