Hahaha...bringing back nightmares from my other life. I will add my 2 cents here on those cams.
IF the config tool he was using says they were already initialized with that IP address, Most likely those cams were tested someplace else on that subnet, he claims they never saw daylight until now?
Its odd that its showing a (not default) default IP Addy. I do remember a time I had issues with those cams or something close to that model and year. Some even shared the same Mac address.
So isolation here key. PC or laptop, power injector or POE switch or wall wart powering that cam. Completely off any network. Set the pc on the same subnet (STATIC) as the cams. Make sure you can ping it
and try to log in. The first thing or one of the first things it should complain about is downloading a plugin? is that happening ? If you are using a modern PC without IE, It won't Install and without that
you will get odd things with your controls, and things will not be working correct or even give you bad info. It sounds like the cams are already set to a static IP address.
You may have to use edge and add that IP address (of the camera) to IE Legacy mode to even try to make it work. Without those plugins working you just might be seeing whats not really there.
Hopefully your modern Version of windows does not just delete or red flag the plugin as a worm or virus, you might have to beg your computer to let it install.
BTW, If you had installed any other "NEWISH" Dahua cams on that same computer, you might have to go to a webrec folder and delete it...naaa wait just rename it and let the plugin reinstall its thing. They get confused ya know sometimes and need a little
kick in the ass to get going.
Perhaps you already did this stuff but getting back to basics is key, with issues like this can be a rabbit hole (Believe me I lived in a few). The reason I mention isolation is because I remember some of these cams were reporting incorrect info
to my router and or my router was seeing them twice...cannot really remember but it was messing with things adding to the confusion.