In the photo it illustrates Master Hwa using "Cai" or "Yank" at the same time he kicks at Tom. In the Tai Chi form there are several different moves to practice "Cai" and some of those have slightly different applications.
In this Youtube video (click the link please) I present a clip of a 2011 workshop. In the clip, Master Hwa talks quite extensively about the difficulties one faces in learning. He also discusses "economy" of learning. Practicing the movements from the "kicking" section of the form one sees a good example of this economizing. Namely, the hand movements practice "Cai" or yanking, while the foot movements practice the kicking routine. He points out that many movements in the form are designed this way. In other words, one limb practices a move for a particular purpose, while the other limbs practice for some other purpose. This is indeed a very economical design that packs much practice opportunity into the 108 Long Form.
Now, as to delivery of power or Fajin:
I recommend the learning of any movements with the same structured approach. I would learn direction, hand/foot position, timing, internal discipline for any posture in that specific order. It makes no sense to start doing a kind of silly attempt at Fajin for a posture if one has incorrect hand or foot position for instance. I say "sillified" because as we already talk about how hard Tai Chi is, one's efforts will be compounded if there is no logical progression to learning.
So, for the kicking section, one has to know what direction(s) they will both move and kick in. Master Hwa talks about keeping one's balance while both kicking and yanking. If one does not have direction, hand or foot position, and timing, it stands to reason there is probably some balance issues involved in the fault. In other words it is hard enough to stay balanced while standing on one foot, much less complete a yanking movement with the arms...don't fool yourself that you "got it". Particularly so if you keep losing your balance every time a shoddy "fajin" yank results while you are kicking.
You can break down the kicking and just practice kicking with no use of arms. Then when you get good to very good balance... add in the "Cai" movement. Keep putting the cart before the horse only confuses the horse does it not? One ends up going nowhere very fast.