2000 Honda Odyssey P1456

Probably - loose or improper seal on gas cap - wrong gas cap. If you left it loose after filling (at least 3 clicks tight) it may have triggered the light. If it was loose, but is now tight, it will turn itself off after several drive cycles.

Could be - a small leak in the evaporative system - part of the emissions system. If so, this will not repair itself and you will most likely be visiting the repair shop.