It says "up to half". This is kind of a tough number to get a handle on and it depends on how you look at it and what time frame. At this moment, of the people who have had COVID, only 11% currently have long COVID symptoms and an additional 17% have HAD long COVID at some point, so that's 28%. Most people who get long COVID have their symptoms resolve within a year.

But in June of 22, that number was 35% (19% current 16% ever).

So it may be based on a specific time period during a certain outbreak.

But again, the vast majority of long COVID cases resolve within a year.

Source: Kaiser Family Foundation

Edit: I forgot to mention, there's also been some discussion that a large number of long COVID cases go unreported. My own daughter had long COVID and we never reported it. It was mild and it eventually resolved itself, but we never took her to a doctor for it, so it never ended up in the stats, so that might be factored in as well.