Peter, No need to get closer. I presume Auto Focus was used and this nearly always tries to focus on the closest object, in this case the nose!

I have the APO Version of the Sigma Lens you have and found this to be the same. I spent a few sessions with local Squirrels and found that by using only 1 AF spot and focus over the eye, quickly recompose and firing off the shot works well. DOF at 300mm is rather thin!

Nice shot though, looking forward to seeing Nik's sharpened re work.