Is it reasonable to assume this is only the tip of the iceberg, as majority could be properly transcribed by voice recognition?
Yes, it is.
I once worked for a company under contract for Google. They also offered work for Microsoft, Apple etc.
Tasks were to rate voice or written requests in Google Search or Assistant in terms of recognizability for the search engine.
I witnessed almost everything from standard searches to hard porn or violence.
For me as a contractor the user requests weren’t connected to the users ID or account, but for the company they were.