I made my comment about K9’s because I worked with them in the military. In the 3+ yrs I did so none of the dogs in my Squad or any other I was aware of (United Kingdom) were involved in instances as you describe.
This does not mean some fools were not bitten who believed they could pet the “nice doggie”. That did happen and those bitten were themselves in the military but like the man said, “you can’t fix stupid”.
Mind you, the statistics work out to be roughly one unintended bite per dog in service per three years, or twisted the other way, over a K9’s working life, odds are that there will be three non-directed bites. (and one in a thousand K9’s do not return to the handler.) There is no breakdown for dogs which are tracking, bomb detection, etc (and when the numbers were first reported, the objection was that contraband and tracking dogs were included, rather than just those which are solely used in the field as K9 Officers to help catch and contain criminals.)
DOJ guidance is now to use as long of a tether as the handler is comfortable using and still control the animal and that untethered K9’s should only be deployed when less than lethal options aren't a logical choice. (And many departments have evolved their policies to only deploy an untethered K9 for felony arrests.)
And I'd like to have seen the FBI report actually include breeds, as it would have helped identify a breakdown of which types of police dogs are most likely to do an undirected bite. A friend in a metropolitan department says that he knows for a fact (ha) that most of his department's undirected bites are munitions detection dogs (and another friend blames the front line officer dogs...)