Writing a letter might be a good idea

I think you need know couple things:

1) The walkway is a public easement, even it is part of private property, the owner could not block your kid with no reason,  otherwise, it is somekind decrimination

2) He might have some evidence that your kid did something improper, you need communicate with him to see what happened. I lived in Texas many years, and I don't  feel it is  a good way to call them Red Neck

3)  He should have talked with you rather than with your kid  for the issue he raised.  It is somekind of harassment in my opinion. It is also your responsibility to understand what happened and educate your kid.