How does that make it STEM? If I study social science and use math does that make social science stem? Or does it mean you used a lot of modelling in a non stem subject?

Social science is STEM by definition. The S stands for science.

you can name anything anything. Rename astrology as future science and that doesn't make it science. Social science is science like or science-y, but not science. Same with economics. They are heavy in math. They are math adjacent. They are not the study of math. They are a not a science. They are not engineering. economics is not STEM and grouping it with stem is weird.

Just because something has science in it doesn’t mean it actually is science. Political science, metaphysical science, spiritual science etc.