I'm inclined to concur with that estimate. I've seen mature (breeding) Wilson's warbler maybe half a dozen times and juvenile maybe twice before the posted specimen. I've never managed to get close enough with my 70-200mm to refrain from cropping with heavy machinery, which does not produce really fine results with my sensor. I would have needed a better sensor, such as an FX model, or a lot more pixels, like the pixel density offered my some mid-range Nikon models. Also, when I see a Wilson's it is always lurking in the gloom of leaf cover and my resultant image is more chiaroscuro than reference book quality.
Vireos are easier to get close to. This one even flew right in to apparently check me out. It didn't feed or fart, just acted as if curious, never having seen a two-headed birder before.

Juvenile Warbling Vireo