It's not a public health issue though, it's essentially a labelling one. There are tests in place to check that things are safe to eat, they just didn't happen to test what it was. Horse meat is eaten in Europe anyway so there's no indication that it won't be safe.
Storm in a teacup really. Ultimately finding you've eaten one herbivore prey animal instead of another is not really a big deal. It's only an issue in the UK because after the BSE thing a few years back retailers are supposed to be able to track their meat to source, rather than tracking it to horse.