The idea in all these MD-family (which SHA1 and SHA2 are members of) collisions is the same, using one or two input blocks you trap the hash function in an awkward place so that fewer state bits than normal matter, and then skewered in this way you calculate one final block that will collide it. The SHA-1DC is watching for that situation which its developers call a "disturbance vector" and so it will detect all attacks based on the same approach and "fix" the hash at a small CPU premium for all hashes.

We know for MD5 that independent (presumably nation state given the costs) elements did a similar but different attack that we only found out about after the published MD5 collision - but it trips the same detection (for MD5 in that case) because it's based on the same mathematical approach, even though none of the actual hash values involved were the same. A defence of this sort would have worked, even against an adversary with nation state resources (in this case probably Israel or the US).