Tail wagging in a lizard, like a dragon or monitor or skink, usually means it's displaying it's alert and perhaps really enjoying something it's doing (usually seen when eating).
I've seen eastern water skinks, delicate skinks, rainbow skinks, 5 lined grass skinks, eastern and central and lawsons bearded dragons , jacky dragons, nobbi dragons, water monitors, lace monitors , sand monitors and others all doing this in the wild.
They can be very expressive with their tails.