[78-L] Columbia 1950s demo

[Han Enderman]

Ebay # 370272615438 shows a Columbia "360" demonstration record, with 5 tracks from LPs, listed as 10" 78.
Numbered 41662, it is a very high nr for the 1950s 78rpm series.
Last Canadian Co known to me is 41476.

What is "360" (early surround?) ?
Why a 78 to demonstrate LP issues? Or is this a 10" demo LP as suggested by the LP logo?
But I have never seen 10" Columbia LPs without prefix, and thus, what numerical series is this?

So what is this?

Han Enderman