Techmarines start with one common craftmanship cybernetic, Later they may upgrade an existing "system" or add a new "bionic".

Is this only a question of diction (writing style), not repating the word cybernetic too often, or ist there an intentional difference between "Cybernetic" an "bionic systems? Personally I see no reason for the later.

Thanks for your opinions.

Its simply a slip of the toungue. Bionics are a term for cybernetic enhancments in 40k.

So, cybernetics = bionics, and bionics = cybernetics.