From yesterdays' email:

"This year, we’re encouraging low- and non-code contributions so more people can do their part for open source regardless of their technical experience."

But at least:

"Hacktoberfest is all about meaningful contributions to open-source projects, therefore, contributors with 2+ spammy PR/MRs will be immediately disqualified"

And projects opt in with the "hacktoberfest" tag to qualify for low-[quality] contributions.