"Art is subjective" is generally understood to mean that the viewer's response to art is subjective. This is demonstrably true. If it weren't, everyone would like and dislike the same art.

I'm curious what you took it to mean -- not the phrase itself, but the purpose of having it in the information about the community. In that context, if it isn't a reminder to be kind to one another even when we don't care for each other's art, then what do you think was meant by it?