An article about this bird can be read
here.
The article seems very reasonable to me, and largely sticks to the facts (though it seems that they couldn't resist mentioning the possibility that the owl
might have taken cats as prey

).
A website that campaigns for raptor protection (with links to the facebook group mentioned by Dave) disagrees though, I guess because the story doesn't fit with their predetermined ideas:
"
...but be warned the article contains a lot of journalistic licence most of which is not factual. For instance the rediculas claim eagle owls can kill large animal such as deer which of course is complete rubbish. The next thing someone will be claiming is they have witnessed an eagle owl carrying off a baby! Why must everyone automatically believe any eagle owl they see in the natural environment is an escapee? Isn’t it just possible to be a bird which originated and fledged from a nest in the wild? After all it was only a few years ago one of the 2007 fledglings from the Bowland nest was found dead south of Edinburgh."
Deer
have been recorded as having been taken as prey by Eagle Owls (admittedly small deer, usually the fawns of smaller species), and the reasons for the assumption that this particular owl is an escape are explained very well in the article.
Although the raptor website campaigns for many very valid causes they are certainly not adverse to use "journalistic licence", and statements that are "not factual" in their own articles to gain support for their views - and personally I have no doubt that they would actually gain far more support if they tried to leave out their obvious biased and incorrect claims from what they write.