What is this sort of abstract rainbow?

This is not a "rainbow". Quoting from the linked site, "not all colored patches in the sky are rainbows". It instead is a circumhorizon arc. Rainbows are caused by internal by refraction and reflection in water droplets. Halos such as the circumhorizon arc portrayed in the question are caused by internal refraction and reflection in ice crystals.

that type of rainbow is created by light refraction within an extended cloud or layer of ice crystals, in which the crystals are similarly-shaped and have been aligned by wind shear so their principal axies are all pointing in more or less the same direction. they then behave like a cloud of microscopic prisms suspended in the air and if you are observing them from the right angle on the ground, you'll see the rainbow.