I think he's just giving a general way to view recovery and knowing when to 'try to push' and when you are trying to 'do enough'. So if he starts his workout and his HR during is lower than usual, and the first couple of lactate tests on that day are low and stable, he knows he can, if he wants, extend that session (say 50-60 minutes). If he warms up and his HR is already elevated 5-10 beats, and the first test comes back fairly high, hey this might be a day to do just what you need to (25-30 minutes). HR and lactate will track, but some days they arent the same. Some days you are feeling good, your HR is high and your lactate # is lower than usual. Others, just the opposite. Depends on time of day, hydration, fueling, previous days workload, etc.
Better trained athletes are having a threshold occur at a higher % of their VO2max (effectively they've pushed their curve/LT2 line further to the right) and thus the HR associated with their threshold will be a higher percentage of the HRMAX. Say you just started base -- your maxHR wont change, lets say its 190. When you start base, with little threshold training, your threshold occurs at lets says 165. After weeks of training at LT your LT may occur at 170, especially after you have added more traditional intervals/speed.