For the second part: you have less chance of removing the whole unit, because the blast template only covers a portion of it, with less chance of rolling a 6 and the entire unit thus being removed, because the template covers, at best with Taloi base size, 2 models assuming you roll better than 1 for the average number of stomps.
The chance of all stomps being kerrunch, i.e. the whole unit covered in templates after rolling a 3 for the number of stomps, is roughly 1 in 500, which would be sufficient to kill the entire unit one go. The chance of one template (i.e. two guys) getting kerrunched is about one in six factoring the d3 roll, better if the templates overlap, but worse again on account of the fact the Knights D attack will remove a Talos of my choosing in btb; assuming he does enough to kill one which is likely. Conversely the probability of me rolling a 6 on one of my three pens against a Knight charging through terrain and the resultant pen rolling d3 hull points is also about 1 in 6.
What this means is, the odds are heavily in your favour if you engage one at a time, which is possible given the glaring weakness of a Knight i.e. MTC. First part: as mentioned previously, The Knight player ended up charging the Claw one at a time on account of, the other weakness of a Knight, abysmal MTC.