Having departed LAX to the west with an easterly destination many times I would say it is almost entirely normal to be given this exact instruction.
Initial call to Socally results in “Maintain 280 knots” then when leaving 10000’ asked to “resume normal speed”.
Its the only place in the country where I see this routinely occur.
I have spoken to an ATCer several years ago who worked under the impression there is a waiver for speed below 10k off the coast to accommodate heavies with a westerly departure to permit flap retraction to clean speed.
The instructions certainly sound to me to imply an authorization to 280 knots below 10k.