The full solution is below, with a short explanation for each group. To avoid spoilers, play the puzzle or open the hints page before reading the answer panels.
GAFFER, EDITOR, DIRECTOR, and PRODUCER all fit the category "Film crew roles". They appear in movie credits. The shared link accounts for all four words, which is why the remaining board words should be tested against a different rule.
Category
Airport words
GATE / LUGGAGE / RUNWAY / BOARDING
GATE, LUGGAGE, RUNWAY, and BOARDING all fit the category "Airport words". Travel days are full of these. The shared link accounts for all four words, which is why the remaining board words should be tested against a different rule.
Category
Things with tails
KITE / MOUSE / COIN / COMET
KITE, MOUSE, COIN, and COMET all fit the category "Things with tails". Each can have or refer to a tail. The shared link accounts for all four words, which is why the remaining board words should be tested against a different rule.
Category
Night sky
ORION / NEBULA / METEOR / VENUS
ORION, NEBULA, METEOR, and VENUS all fit the category "Night sky". Look up after sunset. The shared link accounts for all four words, which is why the remaining board words should be tested against a different rule.