Why are the conditions for a changedelete sign the way they are?

[Vinzent03]

I'm currently trying to understand what a changedelete sign exactly means. The code describes a changedelete as either the last line of a hunk where more lines were deleted than added, or all lines in a change hunk and the previous hunk is a topdelete.

    local changedelete = hunk.type == 'change'
      and (removed > added and lnum == cend or prev_hunk and prev_hunk.added.start == 0)

https://github.com/lewis6991/gitsigns.nvim/blob/main/lua/gitsigns/hunks.lua#L272-L272

I get the first condition to mark a hunk has more deletions than additions, but what is the reason for the second conditions. What makes a topdelete so special that any arbitrary change hunk is considered a changedelete?

[lewis6991]

Open a file without any changes. Delete the top line and edit the next. Without this condition, the sign becomes change instead of changedelete.

press ddx

without term:

with term:

It's basically an edge case as start == 0 it outside the visible buffer and the term says there was a previous hunk at line 0 which can only be a deletion (I think).