Davy

Factory Workshop Manuals, as the name suggests are for the use by authorised dealers and service centres and they're supplied by the manufacturer and circulated among these parties only. This is because the manufacturer usually gets a cut from vehicle services through dealers and agents after their cars are sold (spares mainly). So although we're able to find workshop manuals online, they're technically copyrighted and cannot be circulated publicly. I believe the manufacturer supplies special tools and diagnostic equipment to these dealers as the manuals usually indicate tools required. 

Haynes is a third party company that print their own versions of manuals and they're available to be purchased and used by anyone. I believe some of the content (torque specifications, capacities and tolerances) are obtained from the respective manufacturers. The manuals are usually assuming that special tools (only available with the authorised dealers) are not available and are written with the regular person in mind. Some of the manuals even cover common issues and things to look out for in certain cars - content that's not available in Factory Workshop Manuals 

Hope this makes sense. 

I did not know of this guy. So did a search. guess what, he was actually born in Sri Lanka. 

https://www.google.com/amp/s/www.bbc.com/news/amp/uk-england-47

Thanks @Davy. Found an ETCG video explaining the difference