Spider-Man: No Way Home is the third Spider-Man film in the ongoing Marvel Cinematic Universe (MCU). This film closes the introductory arc for the fan favorite Peter Parker as he finally begins to enter adulthood and become the Spider-Man that everybody recognizes from the comic books.
The cameo, for those who don't know, is a callback to the first Spider-Man film starring Tom Holland. The cameo shows Gary Weeks' Agent Foster, who is partially responsible for creating the Vulture. He appeared in the opening scene of Spider-Man: Homecoming, where Michael Keaton's Vulture was kicked off site by an organization called Damage Control. Agent Foster was the one to give Vulture the bad news, and from there Agent Foster's organization was responsible for taking over the cleanup of the Battle of New York's aftermath.
These events caused Toomes to become the villain Vulture, so seeing this character return is a callback to the beginning of the trilogy. The Damage Control character's cameo happens in a very quick shot, and the above image showcases where fans can see it. Everybody has an origin, but for villains it's typically when somebody does them wrong, and in this case it was Agent Foster.
It's an exaggerated example of why people should be careful of what they say to people. It's unlikely that somebody is going to become the Vulture in real life, but it was still very cool for the filmmakers to show how he took one conversation in a very bad way. It's typical in comics, anime and even video games for the villain to let one thing that happened to them affect them worse than it probably should've. However, it's slightly based in reality, as everyone reacts to things differently.
Marvel Studios is good at doing nice callbacks to minor characters, and a lot of times it takes a very watchful eye to spot them. Many times, these movies offer a lot of potential for being watched multiple times past the first viewing. Hopefully Marvel Studios continues to do this, especially with the upcoming Doctor Strange sequel, which is set to heavily feature Easter eggs as well as new and returning characters.
Spider-Man: No Way Home is currently available on digital platforms.