Resaved it with PaintShop Pro 9,01 - 21,368 bytes.
Then resaved both files with WA - 17,445 bytes, both files.
BMP (uncompressed image) takes 16,588,854 bytes.

Resaved thee original with Windows Paint - 43,228 bytes.

There is no apparent reason for 5MB of the original. Inside it looks like this:

Yes, hex editor says this is uncompressed but indexed image. I suggest a replacement of the original with what WA puts out.


EDIT:

There is no uncompressed variant of PNG.  It is possible to store uncompressed data by using only uncompressed deflate blocks (a feature normally used to guarantee that deflate does not make incompressible data much larger)

So i guess egg somehow used an image editor that supports such a storage method.