Obviously plantbasedanuary isn't as catchy, but if you're only doing it for a month, you can hardly call it vegan.
Veganism is a way of living which seeks to exclude, as far as is possible and practicable, all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose.
Is this really what people are doing for January, or just eating fake meat burgers instead of real meat burgers? Before going back to eating real meat burgers in February. Unless it inspires you to continue with veganism in which case kudos to you.