An APIC with 2 network connections is running with an Active-Standby connectivity scenario.
Because it discovered L1 first, that NIC is in the Active state which means that the other connection is in Standby.
Once L1 is acknowledged, it will find S1 and so forth using a cascading discovery process via LLDP/DHCP.

APICs are equipped with two Network Interface Cards (NICs) for fabric connectivity. These NICs should be connected to different leaf nodes for redundancy. APIC connectivity is automatically configured for active-backup teaming, which means that only one interface is active at any given time. You can verify (but not modify) this configuration from the Bash shell under /proc/net/bonding.