UnBound vs. AdGuardHome and Wireguard DNS setting

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Background: 
I was using Unbound for all blocking and DNS resolution, then switched to Adguard Home for this and only use Unbound for local resolution on 53530.  I had a previously working WireGuard setup using a very basic road warrior configuration for phone / laptop. The DNS server in this configuration was set to my LAN DNS IP (172.27.7.1). 

Issue:
Having not been out of the house since I made the change I noticed that DNS resolution was completely broken on my devices via the remote VPN connection.  After checking a few common culprits, reviewing FW rules, etc. I changed the WG client DNS IP address from the LAN DNS IP to the VPN DNS IP scheme (172.27.2.1) and this immediately resolved the issue. 

Question:
I am just curious if someone with some knowledge of the logic behind AGH can explain why the LAN DNS IP is no longer reachable for DNS resolution?  Is it an ordering issue, how AGH handles the routing?
I mostly just want to understand what the difference is between how Unbound was handling this behind the scenes and how AGH is doing it differently?

I found this Reddit post https://www.reddit.com/r/opnsense/comments/10md5bf/wireguard_not_working_with_adguard_home/ and forum post https://forum.opnsense.org/index.php?topic=22409.msg140811#msg140811 AFTER figuring out the resolution issue, but its just a "Hey, this fixes it" with no explanation of how...

If anyone has some time to drop some knowledge on me, I would appreciate it.