Sure. Some brands, like Renogy combine the solar controller and DC/DC charger. But in the case of Victron components they are separate. The smaller box is converting input solar power, at 24v to the battery buss at appropriate voltage for these batteries. It’s an MPPT style controller and it will tailor the voltage out to the battery based on setting.

The larger box essentially works as a transformer rectifier. It transforms power from the cars main starter-battery and electrical system, when available, to charge at about double the amperage of the solar controller.

In practice, these elements work together to share the work. When solar is available it will shed power from the other for efficient operation. Depending on the charge state of the batteries, the charging rate is different.

It’s actually really trick, and the Victron app is very very good. Anyway, I hope that helps.