Yes, that includes any file uploaded to the game page, now or in the future.
The developer in question was probably using files with special prices, which are often abused to everyone's confusion.
files with special prices
This is what I though and understood the first time as well. The way you phrased it. That you can buy the files. You can't. Your payment level of your purchased project, that you now own in your library, is compared to the payment level of the files when trying to download. This does not affect updates in any way. Except if one would set a different level for new files.
Maybe this is a translation issue. But I think this is very ambigous in English as well.
Imho it is less of an abuse and more of a problematic feature design and naming.