I know exactly what you are saying, if I were to be deleting photos from my photos app, while sync'd to iCloud.
What I'm not clear on, is if you understand what the 'manage storage' setting is doing (as you never referred to it).
For example, the iPhone (with optimized storage) is constantly 'deleting' photos from your iPhone. But it keeps them on iCould (and a thumbnail on your iPhone). This is what @razmee209 had neglected to address... a delete from iPhone is not necessary a delete from iCloud (in this case it was, see below).
That being said. To be safe, I have:
- I turned off iCloud sync.
-- you get "this delete from iPhone but not iCloud" -- Excellent news!
- use storage manager to delete videos -- got free space, yay!
- check photos -- videos are gone, boo
- check iCloud -- videos are there, yay!
@razmee209, you seemed to be right that it would have removed my videos from iCloud, had I left the sync on.
A little more control and verboseness would be useful here.