1) All clinically treated hypertensive patients were excluded - that means if you have kidney or vascular disease (hypertension) and are being treated for it, you aren't counted here. Doctors WILL care about your salt intake if you have these conditions, as they should! It is very common to prescribe something called the DASH diet to lower sodium intake and increase potassium intake.
2) If you're healthy, it means your kidneys are healthy (simplifying). One of the purposes of the kidneys is to maintain homeostatic blood pressure by excreting a combination of salt and water. To put it simply, if you eat a huge load of NaCl, say in a dominoes pizza, your blood pressure WILL NOT be affected for a very long time. I'd guess 20 minutes or so after the salt enters your bloodstream. Which means these folks can't measure that blood pressure change by testing blood pressure yearly.
3) Either medical doctors or the press that listens to them have a nasty habit of taking treatments that often work for very sick people - morbidly obese, type 1 diabetics, bed-ridden centenarians - and applying it to normal healthy folks. I will go out on a limb and say that these unilateral recommendations are almost all BS, and should be ignored. If you're healthy: eating eggs will not affect your cholesterol, eating cheesecake will not give you diabetes, sitting in a chair will not misalign your spine. It would be prudent for you to be skeptical when you hear these claims, often on daytime television or on the internet.