Earlier quoted context omitted.
They could have named that 1:1, 1:n, n:m, n:1, but deemed it too old and unfashionable.
Which side is producer and which is consumer? I don't think fashion has anything to do with it.
How do you read "X:Y": "X to Y" or "Y to X"? And how do you treat "to" - as direction from an origin to a destination or vice versa? As in "I send it to you".