Rugged::Commit#diff doesn't seem to return the expected values

The following script walks over a local clone of https://github.com/ruby-gnome2/ruby-gnome2 and for the commits done at or after the day 2016-11-06, it displays the number of diff.

require "rugged"
require "date"

git_dir = "./ruby-gnome2/"

repo = Rugged::Repository.new(git_dir)
walker = Rugged::Walker.new(repo)
walker.sorting(Rugged::SORT_DATE| Rugged::SORT_REVERSE)
walker.push(repo.head.target)

walker.each do |commit|
  c_time = Time.at(commit.time)
  next unless c_time >= Date.new(2016,11,6).to_time

    puts c_time
    puts commit.diff.size
    puts commit.diff.stat.inspect
end

Here is the output:

ruby rugged_log.rb 
2016-11-06 06:25:04 +0100
2463
[2463, 0, 271333]
2016-11-06 06:26:42 +0100
2463
[2463, 0, 271338]
2016-11-06 09:43:32 +0100
2463
[2463, 0, 271338]
2016-11-06 09:43:59 +0100
2463
[2463, 0, 271338]
2016-11-06 13:30:14 +0100
2463
[2463, 0, 271338]
2016-11-06 14:08:08 +0100
2463
[2463, 0, 271340]

This means that for each commit there are 2463 files modified/deleted. The git command git log --name-status --oneline --after="2016-11-05" shows that it is not true:

965f344 Merge pull request #947 from cedlemo/gtk3_setlocale_C
fa07714 Merge pull request #953 from cedlemo/gstreamer_sample_text_color_example_rb
108bee8 Update copyright date
M       gstreamer/sample/text-color-example.rb
8b5b194 Use the method that returns a clock even if the pipeline is not playing
M       gstreamer/sample/text-color-example.rb
a1f5ee5 gi: return value is return type is void but pointer
M       gobject-introspection/lib/gobject-introspection/callable-info.rb
M       gobject-introspection/lib/gobject-introspection/loader.rb
204c40f gi: do nothing for void type return type
M       gobject-introspection/ext/gobject-introspection/rb-gi-argument.c

What am I doing wrong?

Run the supplied Ruby reproduction against the referenced ruby-gnome2 clone, then compare Rugged::Commit#diff and diff.stat with the shown git log output. Trace the Rugged::Commit#diff entry point; no source file or test is named in the issue. Done means explaining the discrepancy or providing behavior and regression coverage that match the intended per-commit diff results.