The precision is likely the default of whatever instrument recorded the timestamps. At this point, however, having to use VARCHARs instead of some native representation of ISO 8601 is entirely the fault of Oracle. It has been a published standard for over 30 years and should be directly supported.
I believe the poster was referring to the trend of casual messaging—not specifically chat—taking on more of a memic composition in the form of images, GIFs, and the like.