- We've already agreed that the vaccine reduces but doesn't eliminate.
- We've already agreed that a vaccinated person that is also a breakthrough case is infectious for some period of time. (Less than an unvaccinated person)
- We've already agreed that a mask reduces spread, not eliminate, and that it's more effective as source control.
- We've already agreed that when there is more spread, there will be more breakthrough cases.
But, now, when we combine all of those somehow we get a different answer.
Since, I read that as: In an area with high spread there will be more breakthrough cases, leading to more vaccinated people being infectious (and probably not knowing it), and that to reduce this, they should wear a mask to reduce spread at the source.
It's unfortunate that "reducing community spread" to stop all of this is a group effort and there's group members who don't want to reduce spread. But, not doing the action doesn't make those people go away or cause the spread to be magically lower.