Yes, correct.
Actually, equation for "Estimated new diff change" is larger, and involves difficulty. But it can be simplified to that simple form.

(D-B)/(C-A)*2016 is time (in seconds) that will be needed for full round, according to current average speed.
60*60*24*14 is ideal time for full round in case if network hash speed does not change. Basically, average hash speed from last round would take this much seconds on current difficulty for this round.

DIF - current difficulty
DIF_NEXT - next difficulty

next difficulty can be calculated from this:
DIF * (60*60*24*14) = DIF_NEXT * ((D-B)/(C-A)*2016)
or
DIF_NEXT = DIF * (60*60*24*14) / ((D-B)/(C-A)*2016)

Increase = (DIF_NEXT - DIF) / DIF
Increase = (DIF * (60*60*24*14) / ((D-B)/(C-A)*2016) - DIF) / DIF

if you simplify last formula then you will get
(target time) / (average time per block * 2016) - 1