That's an argument about definitions; according to Wikipedia the one /u/Large_Dr_Pepper used is more recent

The conventional distinction between X-rays and gamma rays has changed over time. Older literature distinguished between X- and gamma radiation on the basis of wavelength [...]

However, since current artificial sources are now able to duplicate any electromagnetic radiation that originates in the nucleus, as well as far higher energies, the wavelengths characteristic of radioactive gamma ray sources vs. other types now completely overlap. Thus, gamma rays are now usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus.[25][27][28][29]