O. briareus is not found in the Pacific (US West Coast or Indonesia). Most of the animals from LA are from Indonesia but they occasionally have Caribbean animals (Not US West Coast though) and it would not be all that unusual for a mix-up.
Abdopus sp are usually quickly distinguishable from
O. briareus but the nocturnal
Callistoctopus aspilosomatis can sometimes present looks very much like
briareus (
see this image of Beldar). All three have long arms.
Watch for pronounced horns over the eyes for Abdopus. Typical colors will be a tan and dark brown. Sucker tips will be purple WHEN a color is displayed (sucker tips do not always display a color but it appears that when a color is displayed, it is a single color for the species - albeit many species display the same color, purple-blue is common, orange
seems to be common for some cold water animals).
Callistoctopus aspilosomatis will become very nocturnal very quickly. It can display a very, very red with white spots when upset (you might only see this the first week, it is not often displayed) but is more typically a dull reddish brown with smooth skin (See
Puddles journal for typical looks).
Octopus briareus will typically display white but can show peach and occasionally dark brown (but not usually the whole body - see my favorite photo of
Kalypso). I have never noted a sucker ring color but have not payed close enough attention to make an absolute color call

. You will often seen fluorescent green speckles and dark brown around the eyes when unhappy (see
Gallery picture of SueNami)
A couple of photos should help figure out the species.