Concrete head is an affectionate term applied by some old Japanese sensei to people in US companies who, though responsible for driving continuous improvement, were themselves resistant to change anything for any number of reasons.
I’ve run into this a few times, where the “lean guy” for a company is oppositional on any idea that he didn’t come up with. Sometimes it’s subtle and sometimes it’s blatant. Most of the time, I find the resistance is couched in terms of “what if…” For any of us, it’s exceptionally easy to find ways to make any idea seem like it won’t work. All we have to do is ask “what if [insert rare phenomenon] happens?”
Fortunately, in these situations, the leader has usually stepped up and demanded that we make it work. That seems to be the only way to push through the lean concrete head. His boss (her boss) needs to have the will to insist that we drive forward. If the leader defers, it might be best to find someplace else to work.