Is this paragraph truthful?
Yes, but not in the way you think. No CGI was done, merely digital control of still imagery.
The visual images for the Apollo trainers [...] moved to an entirely digital control.
Hijacking MichaelK's link to the NASA site, we find this (emphasis mine):
Requirements for realism increase the complexity of the simulation. For example, when an astronaut fires thrusters, the simulator must activate readouts and lights showing the thrusters firing, fuel reducing, velocity changes, and also show movement in the scene outside the cabin window. In a moving base simulator, such as a simulator in which a spacecraft cabin is suspended on hydraulically moved pylons to enable it to tilt, physical motion must take place. Causing all these things to happen and coordinating them to happen simultaneously is the difficult task of the simulator designer.
Analog computers commonly supported simulation in the 1950s and early 1960s. Having the advantage of great speed, the electronic analog computer fit well into the then analog world of the aircraft cockpit and its displays. By 1961, though, it became obvious that the simulation of a complete orbital mission would be impossible using only analog techniques. The types and number of inputs and calculations stretched the capabilities of such machines so that when NASA defined requirements for Gemini simulators, digital computers dominated the design.
But note that this does not mean that what you saw when looking out of the window of his trainer was digitally created, it was merely digitally controlled. This is not about CGI, this is about making the pre-processed imagery you see when looking out of the window turn according to control inputs.
This is made explicit a bit further down the page (emphasis mine):
Scene depiction in the Gemini era still depended on the use of television cameras and fake "spacescapes", as in aircraft simulators. Models or large photographs of the earth from space provided scenes that were picked up by a television camera on a moving mount. Signals from the computers moved the camera, thus changing the scene visible from the spacecraft "windows," actually CRTs.
The idea that these machines would create photo-realistic imagery on-the-fly is ludicrous if you look at what they were working with at the time:
The sets of computers could communicate among themselves by using 8K words of common memory, where information needed throughout the simulation could be stored. [...] Over 350,000 words of programs and data eventually ran in the two simulators.
They later ran into problems when the DDP-224's had trouble simulating the Apollo Guidance Computer... that's not the kind of hardware that could run CGI of any description.
Are there examples of the quality of this CGI?
No CGI was done. What the computers did was moving a camera pointing at pre-processed still imagery.
Digital image generation did not happen until the Space Shuttle. Same source, emphasis mine:
Actually, the Apollo Mission Simulators were the last of their type in that the analog environment of the spacecraft that dictated hybrid and functional simulations changed to a digital environment that lent itself to full digital simulations for the Shuttle program. Evolution to full digital simulation, including digital imaging of window scenes, meant even more dependence on digital computers. Making the Shuttle a more autonomous and thus more complex spacecraft contributed to a massive increase in the size of the computer systems needed to support simulations.