I think you are mis-reading that web page. It lists everyone who was a burgess from 1619 to 1775, not just the members of the first assembly. John Upton arrived in Jamestown in 1622 on the Bona Nova as a servant. by 1629 he was a member of the House of Burgesses, serving until 1647. His profile is
https://www.wikitree.com/wiki/Upton-2359. He made his will in January, 1651, it was probated in 1652.
There is a category for House of Burgesses, Virginia Colony.