Actually, I'm not sure if this is the preface the OP was talking about, in fact it's not clear to me who the author of it is. There's another preface[0], from the Uranian edition of Animal Farm, that they might have been referring to.

While it does contain some criticism of the the UK, quite expected as Orwell was a socialist, it also doesn't claim that Animal Farm was really about UK, European, or US governments.

EDIT: I found the primary source[1] of the unpublished preface, it does list Orwell as its author.

0: https://www.orwellfoundation.com/the-orwell-foundation/orwel...

1: https://archive.org/details/TheTimesLiterarySupplement1972UK...