Yes, that's true… but in this instance it may not have a fully balanced output. From my memory of 402/404s, the output is 1 earth, 2 earth and 3 hot. Although there may have been a x-former balanced option.
The manual says it has balanced outputs. If they were just ground compensated or even pin 2 or 3 grounded, I wouldn't have commented that it makes no difference.
Something I wish manufacturers would add to equipment which they know will be connected to an insert point is a singls TRS in/out socket. This could be connected to the mixer insert with a standard TRS stereo cable rather than a split cable to two mono plugs.
I have done something similar for a friend in his studio. All of his insertable effects appear as sockets on a patchbay and he just links to them with stereo leads. The main advantage of this is you don't have to work out which plug is the input and which is the output like you do with standard insert cables.
Steve.