Music is not set to sync to ipad, so why is there 3 Gb of audio there

iPad Pro running iOS 11.2.1: 128Gb capacity. iTunes version 12.7.2.60

iPad is set up to sync with movies only - music sync is unchecked. Books and apps are managed via iPad (which by the way, Apple, is a real PAIN in the proverbial).

But according to the little bar chart on the summary screen, there are some 200 songs occupying 3.2 Gb of space on the iPad. Digging in more detail, it appears the offending tracks are some albums downloaded from iTunes store.

If I tick the sync music and selected music/playlists, nothing appears checked under artists or albums.

I've tried a complete restore/reset to no avail; multiple syncs tweaking options under the music tab, but can't seem to free up this 3 Gb of space.