Quickness != top pace/speed
Digby had some of the best lateral quickness and most explosive opening steps of any player in World rugby at the time. Drawing comparisons between CFS and Digby right now other than they're both playing wing, about 5'10-11", and have dark hair is either highly overrating what CFS has done or severely underrating what Digby did.
Digby was a remarkably mediocre rugby player (the guy couldn't even catch a pass half the time, 2 years before winning Super Rugby) who had such a freakish mix of quickness/power/balance that he was in contention for a World XV wing spot for a good few years. CFS just hasn't shown anything close to that athletic dominance since he stopped playing against kids who were still learning how to shave their first chin whiskers.
This isn't even to mention how Digby and CFS have wildly different running styles, which could hugely impact CFS's ability to emulate much of what Digby did off the wing.
CFS runs very high for a 5'11" guy and has a relatively shorter stride, and he runs with his chest over his knees/toes - sometimes far enough that he puts himself off balance and has to catch his weight when he gets arm-tackled or steps at pace.
Digby ran like he was trying to win an Olympic Gold Medal in the "high knees" event. His torso was much more upright when he was running. Combined with his exaggerated knee action and a unique combination of relatively long strides + high stride turnover, this placed his center of gravity somewhere right near his epididymis and allowed him to change direction suddenly too, which is why he was such a nightmare to tackle after 3-4m of running space.
Marshawn Lynch and Digby are the only two guys I can think of off the top of my head that run this way. Both are/were tackle-busting machines, make of that what you will. It's almost as if they are being pulled forward by the power of their strides, as opposed to pushing themselves forwards off the back leg.
It also absolutely fucking torched Digby's knees after a handful of years at the high levels of play, so there's that.
After that trial can't help but agree with Reg that CFS is looking like he belongs strictly in the centers right now, unless we get an unfortunate injury or two to our wingers. CFS is still really young anyway, he needs to string together a season of consistent game time before we can really start taking measure of him against guys who were proven performers in the past.
TL;DR - CFS runs high, Digby ran low. Not enough evidence to prove what CFS is at this level at all really, much less compare him to Digby.