For example, in "SEC v. Jon E. Montroll and Bitfunder", the individual in question was accepting "investments" in his exchange that were clearly securities (probably fitting the definition of a public offering). He also failed to report a massive theft of Bitcoin and misappropriated customer funds.
This guidance does not claim that Bitcoin or Ethereum are securities.
This is the birth of a new industry. It's unregulated, messy, and the massive amounts of money involved have invited all manner of fraudsters and scam artists - just like the stock market did 100 years ago. There will be a regulatory shakeout and we can all hopefully get back to the business of building a useful ecosystem.