That's precisely how I understood it. I presume that when it is clear that the flight can continue to the original destination, a situation where 5 passengers might want to get off at the alternate will cause havoc in terms of handling issues such as baggage, etc.
By the looks of it, this memo is NOT aimed at situations where the flight has diverted and passengers are provided with alternative transport to their destination. As it says clearly, the circumstances of the diversion have changed.