ATC alert to unknown drone activity near Seletar Airport, local flights suspended (with captions)

ATC alert is at 0:20.
SG law says drones are not allowed to be flown within 5km of an aerodrome without permission.
At that time, I did not understand what is ARP (Aerodrome Reference Point). I thought 3.3km was based on outside the airport airspace hence I assumed that circuits could be possible.
I should have also used UTC Zulu time instead of 2.30pm.
Flights were resumed shortly after that on my next call at time 26.
Plane is Seletar Flying Club's C172N (N5748E) from Seletar Airport (WSSL).