Once scrutinized, these phenomena are almost always explained by humans misinterpreting their instruments (either machine readout, or their own eyes).
Honestly, you wouldn't believe how many people report _the moon_ as a UFO because it shows up in an odd place, gets distorted by unique atmospheric conditions, and can appear in different shapes and sizes (moon phase and proximity to Earth).
These people aren't idiots. Their brains evolved to recognize patterns as a survival mechanism. Arguably their pattern recognition is stronger than everybody else's. But when you factor in lack of familiarity with the scientific method, or inclination towards spirituality, or a simple willingness to believe in extraterrestrial life, it's not uncommon to hear stories about ghosts, angels, and aliens.
These stories do not stand up to inquiry. They have been tested time and time again and always fall apart under scrutiny. The reason that Bigfoot photos are always blurry isn't because he's camera shy - it's because when the photos are not blurry, we can clearly see it's not Bigfoot.
NB: I have no problem with believing in alien life in terms of say the Drake equation (statistically, it's probable!). I just find it highly unlikely of such a visitor reaching Earth.