Interesting that views are split on this.
For me I think he did keep within a discussion on military capability, which I don't think is unfair.
All he clarified was that deterrent should not be undermined by a statement that it will never be used. Whilst, yes, there is some politics here, it can be argued it is common logical sense and hence not in itself political.
CDS could equally say advertising your intent, e.g. filing a civil flight plan for a bombing raid would allow the enemy to know you were coming and easily shoot you down, and therefore would be a bad idea. Is that political or just stating the bleeding obvious?
Stating you'll never use the deterrent is daft, even if you hate the idea of the thing. It shows a fundamental lack of understanding of its doctrine, or more to the point not caring at all.