Based on what the sticker says, I think he's reaching.
And while I agree with his reach and the outcome...the way it was done is problematic for me...because it will be used to over-reach in the opposite direction.
There are times when I beleive the "separation of church and state" clause is not used as intended, but rather used by a small minority to actively discriminate against ALL religion.
And since its based (very loosely) on constitutional doctrine, it escapes scrutiny of its real intent which is discrimination. No better than exluding color...and you can see the extreme of the view from dozens of recent posts...the pendulum has swung too far...and this I see as a way to keep it swinging.