According to the exif, both photos had identical exposure settings. That narrows things down to:
- Lens aperture fault (unlikely, that usually results in overexposure)
- Shutter error (also unlikely)
- Body aperture actuator fault
I don't want to jump to conclusions, but the third bullet is the most likely culprit as per the link you referenced above. There is a known problem with both the K-30 and K-50 cameras with premature failure of the aperture and/or mirror controllers. Reports of the problem first surfaced on this site about a year ago and the issue has been the cause of much sorrow.
Since your camera is out of warranty, the cost is about $200 USD if I remember correctly.
Now that I have put you into a panic, checking the lens would still be a good idea. You can check the aperture actuator on the lens by moving it manually with a flick of your finger. The aperture should move smoothly from full open to full closed with no hesitation or sticking. The actuator lever should also be examined for possible physical damage.
Steve