While there are two types of regen, active and passive, that’s not the difference of the two.
Active regen is anytime the truck is actively heating the DPF to clean it. This occurs either every 24 hours of engine run time or when the soot level gets to ~45% on the dash gauge, whichever happens first. Regardless of what triggers the active regen the DPF page tells you a regen is in progress. The 24 hour clock resets at the completion of every active regen.
Passive regen is anytime the DPF is hot enough from the driving conditions to clean itself, this can be continuous or not at all. There are no indications of this (aside from maybe a reduced DPF gauge) and no additional fuel is injected, it’s 100% passive.
When the dash tells you to continue driving you have had failed regen attempts and/or an issue that’s preventing active regen from properly cleaning the DPF. It’s not normal to see the continue driving message.
Not watching the gauge is not why people get the P2459.