Grey catbird in Italy ?

Hallo everyone, I have set up on my balcony a hanging bird feeder with home-made suet and sunflower seed balls. It is regularly visited by great tits, robins  and (unfortunately) very hungry blackbirds. In the last week I have noticed a new visitor: a grey bird just slightly larger than a robin with a weird tail-flicking behaviour and a reddish undertail (which I can distinctly see when it opens its wings and hovers close to the feeder for a few quick pecks at the balls).

I googled it up and it looks exactly like a grey catbird. I live in Milan, Italy, and I take it this bird is American and has been rarely sighted in Europe, the last sighting being in the UK (Cornwall) in October this year ( I have taken a few amateurish photographs with an old camera and I would like to have your opinion on what kind of bird it actually is.