For a daylily that becomes winter dormant to increase to 10 fans from a single fan over winter in zone 4 is surprising. My information about increase in Florida and California is that increase of 8 times is expected by some hybridizers.
How much did the other four seedlings from the cross increase over winter?
When last autumn was it still a single fan?
Did ten fans sprout from below the soil surface this spring or did fewer than ten fans sprout and then the fans which had sprouted divided?
Are the fans quite small in comparison to the fans of the other four seedlings from the same cross?
One thing that may have happened is that effectively the original fan died (the fan's growing point died). When that happens, as long as the rest of the crown is healthy, new buds sprout. Usually just one or two new smaller baby fans appear instead of one larger fan. Sometimes many small fans appear instead of the larger fan. When that happens they are often described as being "grassy" fans because there are many small fans with small leaves and they are tightly bunched together where the original fan would have been.
Are the ten fans each the same size as the fans on the other four seedlings from the cross?
