You can use the infant seat rear facing - no worries.
The second sentance refers to the rear/front facing issue.
I have read simliar informtion on Delta and Southwest. If your unsure hit the webite for your particular airlines. This can help in case of a misinformed FA but I wouldn't worry!
TJ
edited to add the verbage as I was on the American Airlines website anyway:
qoute<<
FAA Approved Infant Seat or Child Restraint Device Seat Locations
If you are using an approved infant seat or child restraint device, please note that it...
May face toward the front or rear of the plane in accordance with instructions on child seat label
May not occupy an exit seat or the row in front of or behind an exit seat
May not occupy the space between a customer and an aisle
end quote<<<
hope this helps