The DFA50mm is plastic but it doesn't feel like a cheapo plastic kit lens, it's well made. My dfa100mm (the non-WR model) has a similar build and has been handled pretty roughly for 8 years with no issues. To each their own though, and the older 50mm macros (or non-macros if you don't need the magnification) are also dandy.
As to second guessing the settings, there's a candle flame in the image and this can limit the shutter speed of the exposure if you're after a certain look. ISO could possibly have been sacrificed in favour of aperture, but the exif on that photo also indicates it was taken with a canon 60d, so it's confusing all around and hard to know what's accurate
.