This is his way of not throwing Carmichael under the bus. I'm sure in a perfect world he would have liked to allow Pete the freedom to make all the decisions and be a minor league version of Sean. He just hasn't been and Allen has to ride this out.
The HC's responsibility is to inject himself when his coaches aren't maximizing a game plan and LEAD the team. DA is not a leader, he was promoted out of a position of relevance (Peter Principle) into a position he lacks the acumen and traits to be successful.
There is more to leadership than being a good eye for talent (which Allen does as a DB coach) or run a decent defense (as DC).
DA's comment further highlights his inadequacies and the reason why he stated the importance of looking forward rather than scrutinizing the previous decision.
My personal belief is that Sean knew this and promoted DA as a means to make himself look better. Granted, I'm cynical of most human intentions...
Someone used a good band analogy on a different post. You can't take the lead singer of a band away, throw in another 'dude' and expect it to be the same band.