He did not, at least, come up with the concept of a folding chair. Chairs for military campaign were around in a folding style prior to Jefferson. In fact, the concept dates back to the Roman military, though their seating was more likely folding stools than a chair with a back. This plate from 1765 shows a few examples and here is a surviving chair from around 1770. British Campaign Furniture: Elegance Under Canvas, 1740-1914 is the only book I know of specifically on the topic, though reproduced manuals on military life from different times exist with plates of campaign furniture. Likely, what the poster was thinking of was Jeffersons work on the swiveling chair, though there is at least one surviving folding chair from Jefferson. Supposedly he popularized that style of chair due to it's use in the White House, but I have not been able to verify that. As well, if you search specifically for "Jefferson chair" a particular type of folding chair which converts into a step-ladder and an ironing board will come up. That is one of the names for that type of chair (also called a Bachelor chair) and there are stories that claim he was the one who invented it. Again, I can't offer up evidence to support that, but that combination of stories is likely what added up to the idea that he invented the folding chair.