Rookie Mistake - Advice Appreciated

Hi all. Getting info for neighbor who looks to have made a huge mistake.

Long story short, he used 10L of undiluted sodium hypochlorite (bleach - I guess) on a small (like 20sqm) driveway and let it sit 2 days. He just pressure washed it away today (which ran down the street and in front of my house) and was proud that he had no lichens but now it looks like his red paving is duller. From what I've read, he did everything wrong.

From your experience, will the red paving slabs keep getting lighter? Will they degrade over time? What other things will happen? Will his surrounding lawn be ruined? Will it affect my lawn across the street? He's a retiree who was trying to save money so didn't want to say anything definitive and scare him as I know nothing but I've looked at how people do it on YouTube before and this looks all wrong - especially the amount, lack of dilution and letting it sit.

Any feedback I can give him is appreciated.