Pitbulls vary from breed to breed. The American Pitbull is banned in this country as they were responsible for a incredibly high number of serious attacks given the relatively small numbers of the dogs in the UK (there are none here at all these days), as are a handful of other breeds.
Staffordshire Pitbulls are a very popular breed in the UK, in contrast, and are one of the friendliest breeds out there.
The fact two dogs killed a prey animal, whilst distressing to the animal's owner (and the animal too!), is hardly a big shocker.