Thermogenic effect of food, or is the heat melting my fat?

So, I've lost 2 pounds in July. How? I don't know, FitDay says I should be on an even keel. Possible answers:

1. I'm burning more calories on my lunchtime walks than I thought.

2. I'm over-estimating the calories I put into FitDay

3. The heat is making me burn more calories to stay cool.

4. Thermogenic Effect of my food.

I like that last one, but I don't think switching from Lean Cuisines to spinach Chickpea curry over Basmati for lunch really made such a difference. And it's not like I've been getting a lot of exercise, I haven't done yoga in over a week, and I've only walked once or twice a week, for a mile and a half at a time. Oh, and those 2 pounds? Put me at 40 pounds under starting weight, 48 under all-time-high.