Being rigorous means following and maintaining standards of scientific research, no matter which approach is adopted.
There is still a tendency, which is often misguided (but not always), to view any research approach outside of the conventional scientific positivist model as "soft", less rigorous and therefore as having less validity.
Part of the solution to addressing this problem, is educating a wider range of people (who may include scientists, policymakers, and activists) about non-positivist research approaches.
The approaches advocated in the research guidance here - such as Participatory Action Research, Citizen Science, Action Research and Grounded Theory - all involve sets of principles and practices that are designed to ensure rigour. Their proponents argue that these are not inferior to scientific research in rigour or validity - instead they are alternative models of science.
Rigour applies to alternative approaches to science, as well as conventional models of science. Doing research to high standards (following the guidance elsewhere in this pattern language!) promotes the reputation of these approaches as well as producing rich and useful knowledge.