It’s a high frequency All-In-One topology system and it does have a 400V bus… 
The same as all devices in the RS range of products.
Just take a look a the Victron training videos about MPPT RS.
You can see there the 400V capacitors and high frequency transformer that galvanically separates the MPPTs and 400 high voltage DC bus from the battery and 48V.
Also you can take a look here: Potential between earth and neutral - #10 by alexpescaru