To dislodge or remove the lens from its breach-lock system mount you need to deliverately press the release button and twist the lens barrel counter-clockwise. Any veteran canon user knows this.
You can knock-off the lens if it was half-hazzardly mounted and not hearing that re-assuring click.
I know I shouldn't be picky, but the Canon FD system was a 'breech-lock'. The EOS system ( and virtually all other systems ) use a bayonet mount.
Originally, yes. Then the FDn lenses became bayonet mounted with a lens release button on the lens, not the body
The breach-lock is a pain in the @$$ IMHO (I still have some old FL stuff that's breech lock).
5D3, 5D2, Sony α6000, S90 | SY14 f/2.8, Ʃ20 f/1.8, 24 f/2.8, 35 f/2, Ʃ35 f/1.4A, 50 f/1.8 I, Ʃ50 f/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200 f/2.8L IS II, 1.4x II, 70-300L, 100-400L | E-mount: SY12 f/2, Ʃ19 & 30 f/2.8 EX DN, 16-70 ZA OSS, 55-210 OSS, Metabones SB | FT-QL, AE-1P | FD(n) & FL lenses