Multidrop system using DS18B20
No, that is not correct. The datasheet specifically explains that READ ROM command can only be used with a single device on bus. But with a single device on bus, you don't even have to use the ROM address.
When there are multiple devices on bus, you must go through the identification process to figure out which ROM IDs there are on the bus, and then each time you want to command a single sensor, it must be selected by sending the ROM address first and then only the selected sensor will listen for the next command.
The ROM ID search procedure is well defined, and even the datasheet points to the application note how to scan the bus for IDs.