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, G16 | EF: SY14/2.8, V20/3.5, 28/2.8 IS, Ʃ35/1.4, 50/1.8, 50/1.8 STM, Ʃ50/1.4 EX, 100/2.8L IS Macro, 16-35/4L IS, 24-105/4L IS, 70-200/2.8L IS II, 1.4x II, 2.0x III, T28-300 VC PZD, 70-300L IS, Ʃ150-600 OS HSM S | E: SY12/2, 35/1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY300/6.3 ED UMC