Need help understanding how my Spectrum Business setup is working

Hi... first post in this sub; normally I'm in the Ubiquiti sub but this topic seems more relevant here.

I have a small office with Spectrum Business cable internet service. I recently upgrade to the the 1Gbit service plan, and they replaced my single cable modem (a Hitron) with a "two-box solution" that consists of a modem and a router (the Sagemcom RAC2V2S). They told me the two boxes were needed since I have a static IP and was at the highest speed tier. They explained that the router had all of its Wi-Fi and routing disabled, so I expected it was basically in bridge mode.

Downstream of this I have a Ubiquiti DreamMachinePro as my own router, with its WAN network setup with the static IP information I was given, and a cable from the UDMP WAN port to one of the 4 LAN ports on the Spectrum router.

I was curious how this was all working, so I plugged my laptop ethernet into one of the other LAN ports on the Spectrum router. Surprisingly, I got a DHCP IP in the 192.168.0.x range assigned, which is also the same range as I use on the UDMP. This was surprising since I expected the Spectrum router to be in bridge mode. Also surprised it was using the same subnet as I use on the UDMP, and wonder if that is cause for concern.

I was able to hit the router IP and login with admin/admin (haha... I later changed this password!)

I see that the Spectrum router has "Dynamic NAT" setup, which I guess is doing 1:1 NAT thru to my UDMP router? So does this mean I am not in double-NAT? I'm not familiar with Dynamic or Static NAT settings on routers, and have only loosely heard about 1:1 NAT.

Here is the Spectrum router configuration screens:

https://imgur.com/a/04kh5f2

(NOTE: I did change the default DHCP range from 192.168.0.x to 192.168.111.x to not conflict with what my own router does)

I guess I'm not sure why I can't just go direct to the Spectrum cable modem while defining the static IP setup in the UDMP's WAN settings. I tried connecting from the modem direct to the UDMP WAN port, but it never linked up.