My question is still why my second sd card gave me a public ip address rather than the dhcp assigned ip from my router?
The OMV image for Raspberries is configured for DHCP so you either get an address from within the 169.254.x.x range (a so called link-local address) or an address provided by an DHCP server. If your OMV server now has an 75.25.xxx.xxx address for your Windows box to be able to access it there must be a route to this address too (usually an 75.25.xxx.xxx address will be routed to the Internet).
Wild guesses are useless so please provide full output from these two commands entered in cmd.exe on Windows: