Oh yes co-design, and many human-centered design methodologies, definitely can be categorized as a form of constructivist learning.
Since with these design methodologies you are including experienced reality as a necessary step to form concepts and generate knowledge (phenomenology) and do experimentations within that reality without a priori generating a hypothesis (action research / grounded theory approach), and study the practical effects (pragmatism) to give rise to a new reality, embedded in a culture/society, social constructivism fits as the basis of your epistemology.
I know I am taking a ‘tight turn’ there and I may not be accurate in all details, since I have only worked with researchers as a student and as a research assistant under professors, but this has become my view of the methodology. It may be helpful to you to read articles by my old professors Caroline Hummels, Kees Overbeeke, and Kees Dorst. For example:
It’s an interesting discussion, I hope you want to continue it here. What are you working on?