Providing an AUR helper is not the same as endorsing any’n’all usage.
Like any tool you need to know where, when and how to use it. The forum and wiki is plastered with statements about the unsupported nature of AUR.
But it seems that users tend to think - oh well - pamac is also an AUR helper - then building packages using AUR is supported by Manjaro.
I see the contradiction as well - nevertheless - the statements quoted in the OP has been part of Manjaro since day one.
What is even more important with relation to Manjaro - AUR build scripts is all created with Arch in mind - which makes it necessary to - from time to time - to remind all forum members and raise awareness of the fact that AUR is unsupported territory.
Even this very category bears the leading topic