Ed knew how one-sided the contract Dexter drew up was.
- We see at the end of the movie that Ed was a combination of Obfuscating Stupidity and Genius Ditz; since Ed knew that Dexter needed the money more than he did, and because he felt responsible for causing Dexter's accident (which is why Dexter needed a job in the first place), he decided to sign the contract anyway and give Dexter most of his bonus money (perhaps he also thought Dexter should get some credit for coming up with the idea of selling food with the sauce on it). He bought Dexter the yo-yo to show that he wasn't upset over the contract, and wanted to help Dexter out and still be friends with Dexter.
Ed is on the spectrum.
- Ed has a very poor grasp of what would be considered appropriate behavior, is extremely literal-minded, and displays almost savant-like skills at things like making a good-tasting sauce or coming up with an infiltration route.