I think you misunderstand, this is the text mode of the Video Graphics Array video chip introduced with the IBM PS/2 (and supported by most later PC video chips

I think you misunderstand, this is the text mode of the Video Graphics Array video chip introduced with the IBM PS/2 (and supported by most later PC video chips), not a protocol of the video connector introduced with the PS/2 which is also called VGA after the first video standard to use it[1]. The actual output to the monitor is analogue RGB video, just like all other output of the Video Graphics Array (or other later video devices using the same connector). [1] Low end PS/2 models used a less capable chip called MCGA with the same connector, but no-one cares about that dead end.