[Moltke]

a = dv/dt²

Where is the energy in that equation?

[LibWhacker]

We can also excerpt comments that are all around and in close proximity to the one you've excerpted that make it pretty clear (to me anyhow) that they are talking about the photons' energy increasing, not the photons' speed...

Particularly intriguing to experimentalists and theorists alike are the two photons carrying the highest energies ever detected from the Crab Nebula

And

When accelerated particles finally gain the energy to escape, some bump into massless, low-temperature photons from the cosmic microwave background and pass a significant part of their energy on to these particles of light.

But I do sympathize. It used to drive me crazy when I was at the university to have gone to all the trouble to learn the precise meaning of various mathematical and physical terms only to have the professors themselves lapse into lazy analogies and not speak precisely, even in the classroom. Very confusing!

Also, the author is almost certainly not a scientist herself, nor even, it appears, a native speaker of the English language. She's just repeating to the best of her ability something a physicist (or grad student?) told her.