When Dewey talks about a discipline, this is exactly what he means. A discipline includes a way of thinking plus a body of agreed upon knowledge which has been organized in accordance with that way of thinking.
From Dewey’s perspective, a discipline is still fluid; it’s useful in the moment and in specific circumstances, and it can be updated to fit new circumstances by any member of the discipline’s community. There are no “gospel truths” or founders with special status. It evolves based on the evolving needs of the community and its individual members.
Using physics as an example, the way physicists see and think about the world—and the organized body of knowledge physicists agree all physicists should know—exist as they are because, over many generations, physicists have found this knowledge and way of thinking most useful. However, that’s something the community agrees upon; it doesn’t exist that way because it’s the most accurate or useful way to describe the physical world. (Many will disagree with that statement, but this is how Dewey sees things.) If things were to change tomorrow, and physicists found that a different way to see and think about the world (or a different body of knowledge or organization scheme) was more helpful, then the discipline of physics should change, too. And the people making those changes are the individuals in the community via discourse.
So this is an example where the notion of discipline, defined as a specialized body of techniques, combined with constrained time available, was forcing a way of thinking as if it is the gospel truth and not doing even that very effectively.
Dewey would say that this is an example of people not being educated in a discipline. A person educated in a discipline should be able to participate in the community as a full member, including the discourse to make changes to the discipline itself. That’s the foundation of a democratic society. And we should also be capable of participating in more than one discipline instead of being funneled into a single discipline.