Why do I need two extra three byte values to make a 222x222 png using imagemagick (and why didn't this surface in 2016? 64 bit boundary issue? Padding issue? Little Endian? Big Endian?)

Why do I need two extra three byte values to make a 222x222 png using imagemagick ?
Again :-) I don’t understand why since 222*222 = 49,284 so I shouldn’t need 49,286 three byte colour values right? Just 49,284 should be sufficient. What am I missing?

Perhaps 64 bit boundary? Or little endian? big endian?

% { printf "P6\n%d %d\n255\n" 222 222 ; \
cat 1st-49284-2020-2019-roland-flickr-average-colours.rgb} \
| magick  - image88.png
magick: unable to read image data\
'/var/folders/h0/m31kq8415wb50xg_7kwk06h40000gn/T/\
magick-2mCuD6a8H66a7qb5_WpeXHJ3uph3P9pv' @\
error/pnm.c/ReadPNMImage/1442.

% { printf "P6\n%d %d\n255\n" 222 222 ; \
cat 1st-49286-2020-2019-roland-flickr-average-colours.rgb} \
| magick  - image88.png
% # no error message i.e. it works!

And why didn’t this surface in 2016’s blog post about this: How to make a PNG file from an RGB file of ASCII Hex Colours made using xxd
And yes I am totally over-analyzing this :-) !