In 20 years Francis Scott Key will not have actually been held prisoner but was a songwriter trying to sell his wares.
I thought the same about the allegation that Sir Walter Raleigh did not spread his cloak for the Queen and he merely "pretended" it was true. Would not he be a contemporaneous source—especially since he included it in his family coat of arm? This comment is based on a LACK of contemporary commentary.
The "pretended" comment is particularly egregious given the lack of facts to back it up. There were no "newspapers" with gossip columns— or anything like them that would have published such gossip—at the time. The closest thing was the posting of Broadsheets with announcements and some news that would be read by someone literate to whoever would listen. Word of mouth would have spread the story of the gallant Raleigh and such "gossip" may not or may not have been written down by any of the diarists of the day.