I think you're talking about "the electron is accelerated at a speed greater than the speed of light in water"? The "in water" is the important bit. Light travels [as measured in a straight line] slower in water due to bouncing off of the water molecules. It's not that light itself is slow it just takes light longer to make it through the water because it takes a longer path.

It goes faster than the speed of light _in water_. While the speed of light in a vacuum is fixed, light will pass slower through different mediums (i.e. it goes slower in water than air, which is how you get refraction).

You can't go faster than the speed of light in a vacuum. But, you can definitely go faster than light in a medium. Speed of light in water, for example, is around 0.75c.

I wondered the same thing, it’s just bad writing