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.
VIOLIN, HOODIE, KITE, and PUPPET all fit the category "Things with strings". A string is part of the object or how it works. The shared link accounts for all four words, which is why the remaining board words should be tested against a different rule.
Category
Tiny units
BYTE / PIXEL / ATOM / SEED
BYTE, PIXEL, ATOM, and SEED all fit the category "Tiny units". Smallness connects them. 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 / METEOR / VENUS / NEBULA
ORION, METEOR, VENUS, and NEBULA 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.
Category
Things that charge
BATTERY / LAWYER / CARD / RHINO
BATTERY, LAWYER, CARD, and RHINO all fit the category "Things that charge". Charge has a different meaning for each. The shared link accounts for all four words, which is why the remaining board words should be tested against a different rule.