This confusion can easily be avoided by putting restriction on companies having the same or similar training name, symbols etc.
This is really almost impossible to achieve as there are just so much companies existing in the US alone, and it's not rare for 2 same companies to have a similar name.
How was this confirm to be the case, like how was the SEC able to find out people were buying the wrong Zoom or they just felt that should be the case since Zoom (the video) has been more in the news lately?.
It's only based on assumption, but it's a fair assumption. The usage of the Zoom(with ticker $ZM) software has been booming due to the pandemic, and the ZOOM Technologies, Inc. company(with ticker $ZOOM, the comany having no connection with the Zoom software) rose a lot in stock price without any fundamental reason.