I really think @PNWjumper hit the nail on the head in this case.
Of course, each horse is an individual and each case should be taken individually. That said, I have seen plenty of young horses (from backyard bred to top of the line breeding programs) that happily cross canter at liberty, never you mind in a small round pen. Some of them are just balanced enough that it doesn’t seem to matter to them that they’re cross firing. Others (specifically, ones being asked to work in tighter figures) simply don’t have the development to sustain themselves in the parameters they’re being asked to operate in. Still others are just at a point in their growth development that they are all kinds of awkward and cross cantering is just a thing. They grow out of it without a problem, but in that moment in time it’s just what they do. Then there are the ones that cross canter because they have poor balance or just struggle to use themselves correctly.
It really, really is going to come down to the horse and who is looking at them. How educated the person’s eye is will come into play (and how risk averse the person is, as well). At the end of the day, I don’t think it’s an automatic red flag if a horse cross canters especially considering how gawky and awkwardly built some young warmbloods can be. While a goodly few may look to be in good balance at 2, there are a fair number that are still in their ugly or out of balance with themselves stage at that age. Six months and some patience could be all that’s necessary for it to resolve itself.