When I was playing last night, two of my zois became best friends and I got this memory. You can see this is in the Friendship section of memories.
In English, Soulmates is exclusively a Romance label. Zois should only get a memory referencing soulmates if it’s when they confess love the first time.
Also, for any Forum staff reading this, can “Translation” be added as a tag for posts? This isn’t a bug or anything, and perhaps it would be helpful to get feedback regarding translation issues. Maybe if players find and report them, it’ll be easier. 
Just a thought, but it would be nice to add that as a tag on this post and potentially others in the future. 