If you are actually productive with your method, then I would advice you to be happy that you dodged a bullet, and it only cost you 3 weeks. Go for another company, and don't chase this one. If, however, they have a point, try to learn some productivity tools to be more efficient before going for the job. In any case, don't think too much about this company, it will just distract you.
I asked my boss, that as a senior dev with over 15 proven experience, he should not stress to much about HOW I do it, just WHAT I deliver, and WHEN it is delivered. I guess that was asking for to much? Or being insubordinate? Anyways, I was told my skills, abilities or personality was not the problem, am just not "a good fit". Why? Because I like firefox, and using text editors (vs code) over IDES (visual studio).