It is certainly correct that DHS, and to some extent our government generally, is known for over-classifying things either out of laziness, desire to avoid embarrassment, or because they believe that anything remotely security related needs to be hidden. As an intelligence analyst, you likely didn't see the misclassified things (I'd imagine roughly everything you did was classified for good reason). It's the political officials who are more likely to over-classify.
That's a fair accusation - you're responsible for increasing the classification of material if you find it to be under-classified, or request a review in the opposite case. So, it wouldn't be surprising if something came across the desk of a decision-maker or the IC's version of middle-management and they selfishly raised its classification hoping it'd be lost in a blackhole for fear of embarrassment, etc.
