You handled it correctly, I think, just moving along and avoiding a conflict.
If you were going to challenge the right to be there, I'd carry the code from TPWD with you on your boat, the phone number in your cell phone of the local game warden and offer to make a call to resolve the dispute. Most guards would likely back off at that point and they rarely have immediate access to the owners of commercial properties, and if they did the owners wouldn't likely know what to do anyway.
Public waters, with several interesting and often conflicting laws applying themselves, deeded land in some cases to the river bed, all sorts of poorly worded case law . . . it keeps the whole thing relatively up in the air.
Here, though, is the essence of it, I think:
On the other hand, say someone's lakefront home is now half under water. Would someone in a boat feel it is right to fish the perimeter of the home? Likely not though I guess it would technically be legal.
No to fences that in anyway obstruct access to or the navigation of public waters. They are not allowed as best I understand under any circumstances.