Sounds like BS to me.
Tip the waitstaff in Osaka, and they will feel insulted.
One would think that liberals, being cultural relativists, would argue that tipping is a cultural act and should conform to the local culture, but that also goes against the other aspect of liberalism, that anything done by commonplace American culture is inherently corrupt, and should be eschewed and replaced by anything liberals say should be the commonplace culture--to be changed at any moment by what liberals decide at that moment should be the commonplace culture.