That was correct, but I got something else wrong - I didn’t notice that the webcam input voltage is 3.3 V whereas USB outputs 5V. Luckily, the webcam seems to have survived, and even worked for a little bit, though it ran pretty hot and had a very low resolution. These things are surprisingly resilient.
Anyway, if you’re working on a project with the webcam, keep this in mind - don’t connect the Vin of the webcam directly to a USB port, regulate it down to 3.3 V first.