Nobody would probably have given it a second thought if the media hadn't mentioned it. Waleses arriving first or entering behind KC3 would have been appropriate either way.
Given the intel the Met clearly had about alleged plans to spook the horses/possibly even climb on the carriages, and then those arrests, the early arrival might have been some kind of Plan B put into place en-route.
I'm sure multiple scenarios were wargamed, and maybe after that one horse was clearly spooked by something, the carriage procession subtly upped their speed. Best to arrive early, etc.
The Waleses may also have been diverted to a different, slightly longer route from KP to WA.
We won't know the truth, and neither will the media, but the latter trying to blame it on the Waleses, and especially those kids, is low even for them.
JMO