A bit of an explanation so the first four panels don't seem so random:

「天高く馬肥ゆる秋」is an idiom that is colloquially referenced as a quip to the increase in appetite with the coming of autumn. However, it originated as a phrase from northern China as a warning for the locals to watch for attacks by Mongol invaders.

The part about the skies getting higher is due to the drying of the air, leading to less humidity and more visibility of the sky. Horses (and other livestock) got fatter because of all the free grazing they did in the summer, making autumn a prime season for raiders to come and steal some quality animals.

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TL;DR version:

- Like many idioms, this one has a story behind it, which is why it may seem random (e.g., "Don't look a gift horse in the mouth").
- Now it just means that people may tend to eat more in autumn.

recklessfirex said:
A bit of an explanation so the first four panels don't seem so random:

「天高く馬肥ゆる秋」is an idiom that is colloquially referenced as a quip to the increase in appetite with the coming of autumn. However, it originated as a phrase from northern China as a warning for the locals to watch for attacks by Mongol invaders.

The part about the skies getting higher is due to the drying of the air, leading to less humidity and more visibility of the sky. Horses (and other livestock) got fatter because of all the free grazing they did in the summer, making autumn a prime season for raiders to come and steal some quality animals.

Thank you for that bit of info n_n