I haven't heard of this - have you got a link to this source?
I've always known HWE to be an optional "opt-in" from existing LTS installations. Which kernel version it is based on a timeline.
I just updated the links for 18.04.2. Oops, thanks for reminding me! Announcements wise, there isn't usually one for point releases unless there's something significant.
We'll need to wait for an update from @Wimpy, our leader. He collaborates with the upstream MATE team and manages the packaging and SRUs.
My guess is that the new 1.20.2 packages are stuck in a SRU approval queue, as we can see Caja for example is available in Bionic (18.04)'s proposed. You can go to Software & Updates under "Developer Options" to enable Pre-released updates but take caution as this is supposed to be for testing, it could wreck your installation!
There's also the possibility someone in the community could put together a PPA with the updated packages.