Steps calorie adjustment

Hi, yesterday I added 2 hours of slow walking to my exercise plan, which amounted to 410 cals used. Later, when I logged on, myfitnesspal had added an extra 110 calories to my exercise calories for 'steps calorie adjustment', making a total of 520 cals used.

The steps were counted by my iphone.

Does this mean that when I had put in 2 hours slow walking, that myfitnesspal had calculated that in total I had used 520 cals that day walking?Or does it mean that I only used 110 calories when I was walking and I should have deleted the 420 cals I had entered?

FYI my phone recorded 4090 steps. I carried it with me for 5 hours yesterday.

Thanks for any replies. I'm just trying to get clear on this.