You had next to no drift at all (only 1 BPM) between the two halves.
To compare the two halves, go to the public page. Click and drag from the end of the test to the 30′ mark. Note the average that’s calculated for the second half. Next, click and drag in the same manner for the first half. Divide the second-half average by the first-half average: 162 / 161 = Damn close to zero.
If you were near/at your anaerobic threshold, then you could get a very similar result. I would follow this up with an anaerobic test to compare the results.
(Heart rates are very individual. ~160 BPM could be AeT for some and AnT for others, so the actual number doesn’t tell us anything unless it’s compared to another data point.)