this is correct statement. Also can be taxed in other countries if they don't have agreement with US government. Thailand does therefore you don't pay tax on US SS in Thailand at least.
I believe when the female office says 'typical tourist' she is thinking that typical tourists statically spend much shorter time all together in Thailand. Even you don't intend to live there, your stats don't look very typical in that sense.
Say my wife does two land border runs, then fly back to her home country, do you think she will have problems when she applies for non-O visa later on or when she tries to enter with non-O at the airport? Another question: do you extend your visa in between your land border runs? (so you do this every 90 days instead of every 60 days?)
Ok, why they are able to do this when immigration is getting tougher? Do they basically 'know someone' who has those stamps? Just trying to gauge the risk to send my wife with this.
Just FYI, Thai embassy in my wife's country (Japan) currently does not seem to issue multi entry visa, only single. Thai government sure makes this visa business so complicated. 😑