If he had a Hensley hitch then it was not installed properly. The hitch WILL NOT allow a trailer to throw any tow vehicle all over the road when being towed if there is tension between the tow vehicle and trailer.
In my opinion, the only way that could happen is if the struts between the hitch head and the frame brackets were not tightened down properly or even not installed. It does not depend at all on the amount of weight distribution. You could even tow without any spring bars attached and it would still not allow the trailer to throw the tow vehicle around.
Barney