I Think the link in the opening post is wrong. I tried the docker hub link in my docker settings and that worked.
I ended up updating Piwigo through the Piwigo gui settings and it seems to have worked. I'm now on 2.10 with the new features. Not sure if this is the correct way to do it with docker though.
I'm having the same issue as Major Tom, my Piwigo is still showing 2.9.5 with the latest update and I'm not getting the new features that 2.10 is supposed to have.
I tried changing to the latest tag but doesn't seem to have done anything(not sure if I did it correctly)
Also, the Dockerhub page is giving a 404 error atm.