> It seems like you have taken offense to the phrase "stores diffs", but I'm not sure why.

Yeah, I'm not sure why it seems that way to you, either.

> the way delta compression works in packfiles might lead me to calling it "storing diffs" in a colloquial setting

We're not discussing some fragment of some historical artifact, one part of a larger manuscript that has been lost or destroyed, with us left at best trying to guess what they meant based on the little that we do have, which amounts to nothing more than the words that you're focusing on here.

Their remarks were situated within a context, and they went on to speak for another hour and a half about the topic. The fullness of that context—which was the basis of my decision to comment—involved that person's very real and very evident overriding familiarity with non-DVCS systems that predate Git and that familiarity being treated as a substitute for being knowledgeable about how Git itself works when discussing it in a conversation about the tradeoffs that different version control systems force you to make.

A common misconception is that git works with diffs as a primary representation of patches, and that's the implied reading of "stores diffs". Yes, git uses diffs as an optimisation for storage but the underlying model is always that of storing whole trees (DAGs of trees, even), so someone talking about it storing diffs is missing something fundamental. Even renames are rederived regularly and not stored as such.

However, context would matter and wasn't provided - without it, we're just guessing.