There is a tension in the interpretation of text messaging. Is it a written record like an email, which is stored and archived? Or is it more like voice conversation; ephemeral and generally not recorded or archived?
For a long time the default behavior of messaging apps was to just hold onto all messages indefinitely. This led a lot of folks in law enforcement to think of them as permanent written records.
The approach in the quote above treats them more like a voice conversation. Anything of significance should be written down in an official way, even if it originated over messaging.