It seems that two of the (as yet) unanswered questions are:
1. Does your neighbour's patio actually raise the original level of the ground? Or...
2. ...was material removed from the top before laying the patio to result in a finished patio which is no higher than what was originally there?
There is one way you might be able to determine that, or at least get some idea: you could try to compare his patio level with his own damp course, if there is one. If there isn't one, then just below the lower cross rail (doorstep) of his door.
If the top of his patio is less than 6 inches from the damp course (or equivalent level) it could indicate a possibility that building the patio raised the original ground level.
I'm not a builder so you need a someone more expert than me to confirm the 6 inch criteria, especially if the property is very old.
I just remember building a patio at my last house (1950s) in ignorance of the risks attached to it ending up only 3 or 4 inches from the damp course.
Fortunately, I found out in time to ensure there was a much lower channel right next to the wall so the DPC was not breached and splash back of heavy rain didn't create a problem But it was not a satisfactory way to build the patio. I could have caused my own house huge problems.
I'm glad we had the whole thing dug out a few years later for a properly built conservatory, so all subsequent damp risks were resolved for us and our subsequent buyers.