So the argument is that people with technical jobs are likely to do technical stuff outside of work? Or at minimum, have the capacity to do so?

I'm skeptical that many recruiters and interviewers will buy into this. Even if you can show that you were contributing to open source projects or tinkering in your garage, there are still a lot of work skills that may have atrophied, like teamwork, writing & documentation, leadership, etc.

Or that technical hirers are less likely to put the same weight on the gap, since there is no training or credentials or best practices to keep up with? Accountants need to know changing laws, other professions require periodic training, etc. IT seems to be more of, "can you and will you do it?"