Every SSID on every radio needs a BSSID. So if you have 8 SSIDs on a dual radio AP, you will have 16 BSSIDs. Think of it like a unique identifier for the SSIDs in the air per radio.
On a controller, you can see them with the command: show ap bss-table:
(Aruba7005-1) #show ap bss-table
fm (forward mode): T-Tunnel, S-Split, D-Decrypt Tunnel, B-Bridge (s-standard, p-persistent, b-backup, a-always), n-anyspot
Aruba AP BSS Table
------------------
bss ess port ip phy type ch/EIRP/max-EIRP cur-cl ap name in-t(s) tot-t mtu acl-state acl fm
--- --- ---- -- --- ---- ---------------- ------ ------- ------- ----- --- --------- --- --
ac:a3:1e:d8:f1:f3 roaming N/A 192.168.31.140 a-VHT ap 40-/22/22 0 AP-215-BG-8f:1e 0 1d:18h:47m:17s 1500 - 2 T
ac:a3:1e:d8:f1:f0 WLAN_WPA2 N/A 192.168.31.140 a-VHT ap 40-/22/22 2 AP-215-BG-8f:1e 0 1d:18h:47m:17s 1500 - 2 T
ac:a3:1e:d8:f1:e0 WLAN_WPA2 N/A 192.168.31.140 g-HT ap 1/6/19 1 AP-215-BG-8f:1e 0 1d:18h:47m:17s 1500 - 2 T
Most APs have a maximum of 16 BSSIDs per AP, that makes the calculation for a 7240: 2048 APs * 16 BSSID per AP = 32k.
That means that in practice there is no limit on the controller on BSSID; not sure why it is listed in the datasheet anyway... You cannot exceed the number anyway...
Don't be confused with maximum clients; this number has nothing to do with that.
As a remark, having 16 SSIDs on an AP will have terrible performance as the overhead of SSID broadcasts will take a very significant amount of Airtime. Try to keep SSIDs to 2 or 3 max (per radio), whenever possible.