How does the distribute leads option work inside of a sequence?

When the distribute leads option is used inside of a sequence, it is random, but equal.

So if you have 900 leads going through a sequence, and 9 team members set to rotate and be assigned as the contact owner, it would simply rotate through each one.

There is not exactly a direct way to see who was assigned each lead, however, you could run a filter on the Contacts Page for Sequence is {Sequence Name} and Contact Owner is {Contact Owner Name} and that would give you some insight.

Once the step is initiated for any particular contact, you will then see the newly assigned Contact Owner as assigned under that property within their Contact Card.