Why are my containers not reachable by other computers on my network?

I’ve been chugging away, developing in containers for a few weeks, and had no problem at all with reaching the web servers running inside them from my host machine. But as soon as I ran into an issue that I needed some others to help me with, I hit a stumbling block: no one but me can access my container’s web server.

docker ps indicates that it should be accessible (I think?):

5d95d5d760bf multitenant "/entrypoint.sh bi..." 2 days ago Up 6 minutes>80/tcp,>443/tcp multitenant

I’m not sure how to diagnose what’s wrong here. One of my colleagues gave me an nmap output:

nmap -Pn <my_hostname>

Starting Nmap 7.01 ( https://nmap.org ) at 2017-04-03 11:02 PDT
Nmap scan report for <my_hostname> (
Host is up (0.00079s latency).
Not shown: 999 filtered ports
22/tcp open  ssh

Nmap done: 1 IP address (1 host up) scanned in 4.33 seconds

Which seems to indicate that the web ports aren’t open on my host machine. But why? This is true even if I disable OSX’s PF firewall, so that doesn’t seem to be the problem. If I nmap myself, it shows all the right ports being open.