I have just realised that I have missed out the last critical step in my thoughts.
Corbyn feels that this, the second criticism of him and his views (potentially labour party policy) by the military, specifically the army, are an attempt to influence the success or failure of his policies. He believes that the military should not do this since it would be the military interfering in the democratic process. I agree with him (on this issue and only on this issue). The military should not interfere in domestic politics.