>Is this motivated by a need to prepare for war?

In short, yes.

>The possibility to pay by card when the internet is not working – ‘so-called offline payments’ – is an area that ‘the Riksbank believes needs to be improved considerably, particularly in light of the geopolitical unease in the world,’ according to the announcement

https://www.riksbank.se/en-gb/press-and-published/notices-an...