Gerry Lindgren's 8:40.0 was not an American Citizen's Record.
On December 5, 1963, the AAU approved Jim Beatty's mark of 8:30.8 as the indoor American two mile record so at least one American had run faster than Lindgren.
In that 8:40 race Lindgren's 3000 meter time of 8:06.3 was a US Citizens record.
Ron Clarke and Gerry Lindgren shared the Outstanding Performer Award for their two mile performances in that February 15, 1964 San Francisco Golden Gate Indoor Meet.
Lindgren's 4:01.5 mile (he placed third) was run in an Invitational meet in Kingston, Jamaica which was held on 8/13/1964 and 8/15/1964. Lindgren also won the three mile in that meet with a 13:17 which bettered the listed American mark and equaled the World Junior Record.