not able to get correct out_skull.surf of fsaverage

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1

I just learn about the tutorial “Head model and forward computation”, which use “sample” to generate a volume src. Here is the plot of sample’s bem.
tutorial of Head model and forward computation

微信图片_202302272213647
微信图片_202302272213647780×260 113 KB

Since I want to get source localization using eeg only, I try to use “fsaverage” to do the same job, so that it can provide the location of montage of “10-20”.
But I get fsaverage’s bem like THAT:
微信图片_20230227213717
微信图片_20230227213717800×215 114 KB

Looks like I got the wrong “outer_skull”, since it was attached to the outer_skin. it’s really different from the plot of tutorial.
Was it right?
here is my code:

surface = 'C:/Users/xuesiyang/mne_data/MNE-fsaverage-data/fsaverage/bem/inner_skull.surf'

plot_bem_kwargs = dict(
    subject='fsaverage', subjects_dir=fs_dir,
    brain_surfaces='white', orientation='coronal',
    slices=[50, 100, 150, 210])

vol_src = mne.setup_volume_source_space(
    subject='fsaverage', subjects_dir=fs_dir, surface=surface,
    add_interpolator=True)  # Just for speed!
print(vol_src)

mne.viz.plot_bem(src=vol_src, **plot_bem_kwargs)