No access to a 2007 but my 2002 has a “reserve” zone on the fuel gauge. I don’t think there’s a warning light or anything else.
There isn’t a valve to switch to reserve manually either. (Unlike most motorcycles I have owned…)
Unless you were riding a steep slope, OR filled up on the side-stand, it isn’t clear why it only swallowed two gallons and change, but there’s always a little fuel left in an “empty” tank that the fuel valve simply reach. I would suggest you run it nearly dry again, or siphon off the fuel and carefully assess the condition of the tank and the intake on the fuel valve. Don’t use a Bic lighter for this…