I imagine it's pretty close.  It says "Americans" and over 25% of Americans are under 18.  Even if all the kids are working, in Nov 2024 there were 209M working age Americans (15 to 64 years of age) with a total population of 345M
 
 I read some interesting stats a while ago while arguing how all American taxpayers had benefited from the TCJA.  The top 50% of all taxpayers paid 97% of all federal individual income taxes.  This means the bottom 50% of taxpayers were only paying 3%.  I don't think 51% of Americans paying no federal income tax is unrealistic... I mean, I buy it.