The Techage web site sorely is lacking in support, IMHO (busted links, links for manuals instead provide firmware, etc.). The best I can tell, the NVR's 'Wi-Fi' is possibly a misnomer, in that it operates in 'Ad-Hoc' mode rather than what we usually associate with the term 'Wi-Fi' wherein it operates in the 'infrastructure' mode.
What this means to you is that the NVR provides a wireless signal ( in Ad-Hoc mode) that connects directly to the IP cams (also in Ad-Hoc mode), and not to your home Wi-Fi (infrastructure mode).
You plug the NVR into your router, install an app on your smartphone and use the app to get the cams to connect to the NVR's wireless. Once all 4 are done you can then unplug the NVR from your router but I have to assume if you do that you would NOT be able to see your cams from outside your home (WAN) and possibly from inside your home (LAN).
The way I see it, and I am making my best guess in all honesty, it's like this:
NVR==>> NVR wireless ==>>CAMS
|| << note 1
ROUTER ==>>ROUTER wireless ==>> smartphone
||
INTERNET ===================>> smartphone
Note that if you disconnect cable 1 above that goes from NVR to ROUTER you won't be able to see cams, surely from outside your home (WAN) and possibly from inside home as well (LAN).