Oh, thats interesting. f/18 makes sense, but I would have guessed that this has been a smaller sensor (the size relation between sensor and subject is what causes depth of field blur). So at f/18 I would expect plenty of loss due to diffraction.
Its interesting! I just used gemini to find out what effective resolution f/18 can produce. Its about 6.5mpx (3,120 × 2,080 pixels). This is just a good to know. I still think that this is a perfect capture!!