This is just a guess, as I have neither kit. But Dragon's 4 figure kits that you can buy as a set usually have the same poses as their box art- Dragon armor kits usually don't come with any figures even though the box art includes them. Because this armor kit comes with two sets of figures- I think their boxart does not correspond with the poses, but instead the figures are posed as they were origionally as a box set.
Generally speaking- I've never come across an older Dragon set that was multiposeable- but some of their new Gen2 sets include different weapons/heads- never extra arms or legs.
That being said Dragon figures are easy to modify (or easier than resin IMO). It probably wouldn't be too hard to get the kit figures looking like those on the box. Especially as the box has 3 figures and the kit comes with 4- you can use the 4th figure for extra parts. Figure modification is just careful planning and a little putty work.