You're probably right, I can't check the TB spec but from what I see in shops I'm gonna say those "passive 1m 40G" cables are manufacturers breaking the spec. I'm also seeing "20G" cables that claim to only do 5G USB3, which is concerning & confusing me quite a bit...
FWIW my confidence level on "would an active TB3 cable work for USB3 if it had the proper bits set" is somewhere along 66% to 75%; this is based on the SERDES in some (most?) TB3 host silicon being able to switch to USB3 to "downgrade" a port... meaning the electrical level can't be all that different... but I haven't dug into this.
While we're at it, I forgot the 2 SBU pins too, so that's 2 extra wires for TypeC-TypeC cables... neither USB nor TB uses them; native DisplayPort does (not including DP over TB)
FWIW my confidence level on "would an active TB3 cable work for USB3 if it had the proper bits set" is somewhere along 66% to 75%; this is based on the SERDES in some (most?) TB3 host silicon being able to switch to USB3 to "downgrade" a port... meaning the electrical level can't be all that different... but I haven't dug into this.