Nothing too unusual here.
Guilty plea often means a comparatively light sentence. It's if you profess innocence and force the prosecutors to go to trial that they will throw the book at you. A lot of innocent people end up pleading guilty on the advice of their lawyer because they'd rather accept a few months in prison than crippling legal costs and ten times as long inside if they lose anyway.
I'm expecting this case to be cited by politicians in future as proof that pornography is addictive and damaging, and the government has to step in and censor the internet to protect people from it.