You have answered your own question. If the load draws only 28.3 amps continuous, with maybe a turn-on surge twice that for 1/2 second, no harm no foul. The breaker is rated to handle brief start-up currents close to 50 amps, not a continuous 50 amps.
For a real 50 amp load you would need 8 gauge THHN wire, but 28.3 amps is ok for a short run of 10 gauge. If the wire gets warm to the touch that is not a fire hazard. I do not see any UL violations here.
NOTE: To answer your 3 extra questions;
1) 10 gauge wire is too small for 28.3 amps continuous load. It will get hot but certain high grades of insulation would not catch fire, but the voltage drop over 3 yards or 3 meters would be a lot. The load dictates the plug and wire used, not the other way around. For a given type of plug a certain range of wire gauges are allowed and maximum breaker amp limits are dictated. The type of breaker panel is determined by summing up all the possible loads it might have, with 120 VAC loads sharing breakers to keep construction cost down.
2) Yes, there is a UL enforced rating for the plug and socket type and the wire gauge, based on the voltage being supplied and the expected maximum continuous load current. We are not dealing with 3-phase or even single phase 600 VAC here, so we can stay with residential sockets and plugs. Dedicated 30 amp breakers for a large kitchen are custom install work hopefully built into the cost of the building. It is expensive to add-on later as it requires using 10 gauge wire, and your breaker panel needs a spare slot for it.
3) There is not always a large gap between a wires amp rating and the breaker protecting it. The best I can say about this is that 240 VAC high-wattage appliances will at least have its own dedicated breaker. That rule does not apply to 120 VAC loads which may share a 15 amp or 20 amp breaker.
The socket and plug and wire have to meet UL ratings for the voltage supplied and if it is single phase 120 VAC or split phase 240 VAC. 240 VAC outlets are large and have big slots and connection slides to handle up to 50 amps typical. This would be your water heater, clothes dryer, etc. Items that consume several kilowatts of power as normal operation. The wire is 10 gauge to 8 gauge and rated for 250 AC.
You can see why normal 120 VAC outlets are simple things, though a ground pin in the socket is mandatory, even if what is plugged in does not need it. Wires can be as small as 18 gauge for desk or reading lamps or 10 gauge for toasters, microwave ovens, etc. The outlets limit is about 1500 watts, and it may share a breaker with another outlet or ceiling lights.
Yes, your breaker panel may not have enough breakers to cover each outlet and ceiling light, so tripping a breaker is common in the USA because contractors do not have to have dedicated breakers for each load. Something that has always annoyed me.