No, only about 10% of billionaires are self made, as in not having inherited wealth or come from wealthy families. And even this is a record high up from a more typical 3%. (and remarkably, these are numbers that forbes feels excited about)
The article explains that they rank the level of "self-made-ness" out of 10, with 10 being from a poor family with no advantages. Then it says " A total of 34 billionaires, or 8.5%, scored as 10s".
Quote from your own source...