From the duplicate I have closed:
Unfortunately, galaxies don't have a neat edge (and the Moon is not at a fixed distance) so your question is difficult to answer in absolute terms.
However, a commonly quoted diameter for the disk of the Andromeda galaxy is something like 70 kpc (about 220,000 light years), which at a distance of 750 kpc (about 2.4 million light years, e.g. see Andromeda galaxy) gives an angular diameter of about 5 degrees, which is about 10 times the diameter of the full Moon.
Thus I think the picture is reasonably justified.
On the other hand, is it realistic to expect to be able to see Andromeda this big? I'm not so sure and have asked a linked question about this.
For example, this (well-known) picture from the digitised sky survey shows an Andromeda disk that is less than 3 degrees across!