Not exactly accurate. If the French triathlon event is sanctioned/permitted by the French federation (FFTri) then under European Tri rules any competitor with a race licence from another federation e.g. BTF can race without that medical sign off. You are assumed to be fit to race by FFtri as you have BTF membership.
Same goes for IM events if they are permitted by the national federation (only US IM events don’t recognise this however).