There are generally two types of fault, those which are "latching" and those "non-latching".
Latching are basically serious or significant issues, principally those which will cause emission control to be compromised. As the name suggests, these cause the MIL to come on and stay on (latch) until someone goes in and cancels it. The MIL stays on even if the original fault goes away on its own.
Non-latching are less significant faults, some which may compromise drivability or emission control to some extent but if the fault goes away (e.g. poor intermittent electrical connection, a sensor slightly out of range etc) and the system returns to normal operation the MIL can cancel on its own. A fault code may well still be stored in the ECU for future reference.
Sounds like you had a non-latching type fault, possibly a hot fuel handling issue for example, which once it cooled and sorted itself means the MIL has gone out again.