BDS seems to open 2 ports per IP.  That's 2 ports for IPv4 and 2 for IPv6.  This is reported in the output as:

[2021-02-22 20:15:24 INFO] Starting Server
[2021-02-22 20:15:24 INFO] Version 1.16.201.3
[2021-02-22 20:15:24 INFO] Session ID a81c2fce-d459-4cc1-a1c0-1e8c9cb097da
[2021-02-22 20:15:24 INFO] Level Name: Bedrock level
[2021-02-22 20:15:24 INFO] Game mode: 0 Survival
[2021-02-22 20:15:24 INFO] Difficulty: 2 NORMAL
[INFO] opening worlds/Bedrock level/db
[INFO] IPv4 supported, port: 21210
[INFO] IPv6 supported, port: 19133
[INFO] IPv4 supported, port: 19132
[INFO] IPv6 supported, port: 54428

Note that I have 
server-port=21210

server-portv6=19133

in my configuration.  So those two ports are expected.  The other two are not.