He is a bit small, but not a big deal (like others have said). My 4 year old male who I've had since hatchling is 1100g, never missed a meal! And my 4 year old female (who should be double the size of males) is only 1300~1400g, and she also has never missed a meal in her entire life until very recently... she ate almost weekly. Sometimes they just stay smaller.
A small rat once every 2 weeks is actually within normal range for an adult male, if they were being honest about the feeding times.
There's also no "need" to mist ball pythons. They just need 50%+ humidity (and 60%+ when in shed), so any way that you can maintain that is good- large water bowl or any other combo of methods. The only reason why people mist is just to up humidity. Misting and making the substrate regularly damp actually isn't good for them either, so just as long as the humidity is appropriate.
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