The issue here is that these works have been in a private library, inaccessible to the public, since the 1930s.
In this case, the author is using "decolonize" to mean to liberate the work from private ownership and make it available to the public.
When "decolonize" is used in the context of e.g. education, it refers to restructuring an education system to be more equitable to all students. As such, the idea of providing access to everyone is a default implication of the term, even if its origin more specifically relates to dismantling the colonial baggage that led to structural inequality.
If that's the case, it seems like jargon for jargon's sake. IMHO that sense would have been much more clearly communicated by using a word like "democratize."
The situation kind of brings to mind slang, where people often invent unneeded new words mainly as a way to signal being fashionable or being part of a group.
The people reacting badly to this are just being somewhere between parochial and bigoted.
"I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail."
The only tool the author of that blog seems to have is their personal ideological beliefs regarding colonialism, thus the author proceeds to treat everything as if it was colonialism.
Honestly, it seems like a faddish buzzword, incorrectly used.
IIRC "decolonizing" sometimes means returning cultural artifacts acquired during colonial times to the regions/cultures where they originated. However, it doesn't make any sense to do that to cultural artifacts created by citizens a colonial power in their own originating culture. Honestly, that sounds like another kind of colonization.
This article seems like a mess trying to force a combination of trendy ideology with personal experience that don't really fit. For instance:
> For her, the archive became a place of postcolonial recovery and remembering.
What's that in reference too? A student seeing a card catalog that's still in use, and being reminded of personally using them in the past. It's weirdly trying to particularize the universal. I'm about the farthest from a "colonized" person there is, but I could have had the exact same reaction to the exact same situation as that student. The only difference is that I have the wrong background, so no one's going to try to gratuitously describe my reaction as something "postcolonial."