Photon’s Presence Changes Atoms Transition Energy?

I read this article in Science Daily and kind of shook my head. I’m hoping a kind and informed reader can explain this to me.

The jest of it is this; scientists have found a way to observe the creation, life, and death of a single photon. Prior to reading this article, I was under the impression that the only way to detect a photon involved it’s being absorbed by an atom raising that atoms energy state (causing an electron to leap to a higher orbit). This article suggests that the mere presence of a photon changes, very slightly, the transition energy of atoms.

I was of the belief that electrons had fixed energy levels and could only jump between them because the “orbit” had to be an integral multiple of the electrons wavelength.

So clearly either this article is bogus, and with yesterday being April Fools, that’s always a possibility; or there is yet another thing about quantum mechanics I was unaware of or failed to grasp.

So, Dear Readers, if you understand how this can happen, please leave a comment with a brief explanation or a pointer to one.

Thank you!