Earlier quoted context omitted.
USCIS calls it a visa in the first sentence: https://www.uscis.gov/working-in-the-united-states/permanent... You may be eligible for an employment-based, first-preference visa if you are a noncitizen of extraordinary ability, are an outstanding professor or researcher, or are a certain multinational executive or manager.
It wouldn't be the first government website with confusing wording. They call it visa, but practically "EB-1 visa" = green card. There's no intermediate stage between the two. There's no sticker on your passport that says EB-1. You can't use your EB-1 status to enter the country or work or anything else. EB-1 simply means that you jump to the front of the line to get a green card.
Also, calling it a visa is misleading. The Green Card gives you the right to reside here permanently and you don't need any visa once you have it. So it's not a visa, and even if it was a visa it would be the Green Card that would be called out, not the bucket through which you get it.