I call BS. Where do these absurd theories come from. A clean chain is a long lasting chain. A dirty chain not only wears out itself, it wears out the freewheel/cassette cogs and chainring teeth as well. These are the sorts of theories that only sound plausible to people that don't ride many miles.

Chains should be replaced when they start to lengthen. The rule of thumb is replace before they hit + 1/16" over 12 links/inches. I swap mine a little earlier.

If a chain noticeably lengthens because you cleaned the dirt out of it (sounds suspicious), it should have been replaced long ago anyway.

Some Shimano chains do have an inner side and an outer side, as noted. There is no forward or reverse direction.