The fuel tank is vented to a closed system to prevent gasoline evaporating into the atmosphere. That system has numerous valves and controls built into it. Essentially, it is still just a vent on the fuel tank though.

The codes the UCrew listed relate to that evaporative control system. The dealer could try and test the system, but it seems they would have had to siphon half your fuel off to do that, and would prefer not to do so. I am just guessing, but I think the test may involve pressurizing the vent system, and they need air space in the tank (not fuel) to do that.

If the light comes back on, drive it until it is down to a half tank and make an appointment at the dealer. If you have to refuel, don't fill it above half until the dealer has done their test.

Don't worry, it doesn't sound major.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue