It's not nonsense - it comes from the standards defined by ISO 2281. A 3 bar watch is considered 'splash resistant', and swimming is not recommended for anything under a 10 bar rating. Start watching at 1:33:Plenty of nonsense heard from this thread. 3 bar are good enough for swimming. But vostok watch are not high reputable for their QC so it's matter of reputation about their QC rather than the spec.
A watch need not bring to deep water 200m deep to do the test but can be done inside a pressure chamber. If a watch is rated to go 30m deep, yes. It shall. I will trust a Casio watch and their recommend.