On an account-based EVM chain such as IoTeX, fan-in means many addresses sending to one, and fan-out means one address paying many. The address format says nothing about either shape.
Counting senders and receivers
The free check counts outgoing transactions only. A hub that pays out to many recipients raises that count. A hub that only collects does not, so read the inbound side in the public record.
Phrasing the pattern
Describe pooling followed by redistribution and attach the hops you resolved. Leave out the word mixer unless your evidence names a service.