Short answer: glitch isn't the right word. There was almost certainly a particle with an extremely high energy. Whether they can measure energies that high is questionable.

Long answer: I'm not familiar with this specific experiment, but I am familiar with ones that try to measure the same thing.

The thing about most of these devices is that they have a sweet spot in which they have the highest accuracy. These detectors have a sweet spot which is a few orders of magnitude below the energy measured here. So there is always the question of how well you can extrapolate.

You'll notice there is no uncertainty quoted on the energy. It would not be unreasonable to expect that uncertainty is at least 1 order of magnitude in each direction. Probably more.

While that might seem like a lot, it's also important to know that the relevant measurement is not the particle's energy, but actually the number of particles above a certain energy. So they don't care so much if the energy measurement is off by a lot, as long as it's really big.