I would say inadequately informed rather than misinformed. The footnotes to the support doc linked above include the statement
Apple Watch Series 2, Apple Watch Series 3, andApple Watch Series 4 have a water resistance rating of 50 meters under ISO standard 22810:2010.
This identifies the testing standard, and that allows correct interpretation of the stated water resistance. The ISO standard specifies a test with static overpressure which doesn’t take account of dynamic pressures due to swimming movements. Like any test of this kind it should also be applied with an appropriate safety margin. You wouldn’t load up a crane to the load for which the wire rope was tested, and the Safe Working Load (or Working Load Limit) marked on the crane will have a significant safety margin maybe up to 20x against the load applied in testing. Safety margin for a watch may be smaller than for a crane because nobody gets hurt if the watch drowns, but the same concept applies.
About Apple Watch water resistance - Apple Support
You have been misinformed. The series 3 watch is not rated as 50 meters at all. In fact Apple recommends only swimming is acceptable.
What is considered “shallow water”?
