The survey presumably doesn't include all the people who work in Greggs* because their CVs went in the bin of employers who demanded graduates. That would leave a cohort of non-graduates whose skills/aptitudes are good enough to get them through the door.
Hang on, it's more confusing than that:
"It found that 48 per cent of developers with less than four years of professional experience currently hold a Computer Science-related undergraduate degree, while 49 per cent had completed an online course instead."
What about the people who had a degree not-in-Compsci and not-online? Is that really only 3%?
Smells fishy to me.
* I've nothing against people working in Greggs, I'm just being flippant.