This is a scene from the world's fair where Steve tried to reenlist for the 5th time. As you can see the "cameo" is actually the original Human Torch, an android also known as John Hammond. Here is some info on the character..
The "Human" Torch was actually an android created by scientist Phineas Horton. He possessed the ability to surround himself with fire and control flames. In his earliest appearances, he was portrayed as a science fiction monstrosity, but quickly became a hero. The Human Torch was one of Timely Comics' three signature characters, along with Captain America and Namor the Sub-Mariner. Like many superheroes, the Human Torch fell into obscurity by the 1950s. In 1961, Marvel recycled his name and powers into a new, unrelated Human Torch, a member of the Fantastic Four (who actually was human). Unlike Captain America and the Sub-Mariner, the original Human Torch has had only a small presence in the post-1950s Marvel comic books and is closely associated with the Golden Age.
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