Nothing you described suggests any engine mechanical problems. All engines consume some oil. The longer you wait between checking, the lower the oil level is going to be. How fast it gets consumed depends on the engine's mechanical condition, how much it's driven and any leaks.
The engine oil lamp works from oil pressure and not necessarily oil level. If the oil light only ever turned on with the " Ignition-On" and " Engine Not Running", then the oil pressure warning system is working properly and, though the level was very low, it was apparently not so low to deprive the engine of oil pressure. Good thing you added oil when you did.
You should check your engine oil level regularly. How frequently would depend on how old the car is and how much you drive, but at least once every month or so if you drive the vehicle every day.