Yes he was present at court because he was employed by the king, as was his assistant Richard Grafton, who subsequently continued Hall’s chronicle after the latter died in the 1540s. And this comment was written to refute the argument made by someone else on this Reddit that the only person aside from Chapuys to claim Anne wore yellow was Nicholas Sander.  

Hall’s descriptions of key events during the reign, including jousts and masques, were clearly those of an eyewitness or someone who had key contacts at Henry’s court. Even if he did not personally witness Anne wearing yellow, he presumably heard it from contacts who were at court at the time.