Why is this NMAP scan to a remote host showing me no ports open when the ports REALLY are open?

filtered

Nmap cannot determine whether the port is open because packet filtering prevents its probes from reaching the port. The filtering could be from a dedicated firewall device, router rules, or host-based firewall software. These ports frustrate attackers because they provide so little information. Sometimes they respond with ICMP error messages such as type 3 code 13 (destination unreachable: communication administratively prohibited), but filters that simply drop probes without responding are far more common. This forces Nmap to retry several times just in case the probe was dropped due to network congestion rather than filtering. This slows down the scan dramatically.

You could ask nmap to try a TCP Connect ...

nmap -PN -sT -p 33491 example.com

Nmap responding that a port is filtered does not mean that it is closed. It means that NMap is not able to make that determination - it could be either open or closed.

Per the manual Chapter 15

Filtered means that a firewall, filter, or other network obstacle is blocking the port so that Nmap cannot tell whether it is open or closed.