What does the level of interactions refer to? (what kind of interaction)
Recent co-workers ahead of past ones, people I met recently ahead of those I met a longer time ago, family ahead of friends and other acquaintances.
I remember thinking: they definitely aggregated a lot of sources to get this list.
Could it be people who searched for you before you made your account?
I've noticed something similar with a handful of people but always assumed they were people who searched for my name and couldn't find me at the time, so their search was put on hold until an account with the corresponding was created.
The people you interact with the most are probably also more likely to be the people that interact with each other. So FB can see everyone who has your email address in their list and then prioritize those people who are most connected with each other.
I am guessing, but it is quite amazing how freakily accurate simple statistics can be.