MacBook – Why does decreasing the brightness cause the brightness to increase occasionally on the MacBook Air

The flicker is caused by the technology (TN) used in your MBA. It's noticeable when brightness is high and under some of the tests. I have 13" MBP 2010 and I can register flicker on 2a and 4a tests when brightness is above 50%.

Usually under normal use this shouldn't be noticeable.

There's a really simple way to test this if you have another Mac, or any other machine really.

Turn on one of the Sharing features on the Mac in question (File Sharing, Remote Login etc.) and try to connect to it from something else. If the entire machine is asleep it won't work. If just the screen is asleep it will.

I assume you're connecting to some kind of wireless network with the MacBookAir, so you could also check the list of connected wireless clients on your router. If the entire machine is asleep it should not be connected. It may still show up in the list of DHCP clients (clients that have requested an address from the router recently), but it should not be connected.