Swimming best speed calculation

Yesterday i did the 100x100m challenge and the summary says:

Avg tempo: 1:40 /100m
Avg moving tempo: 1:24 /100m
Best tempo: 1:01 /100m

But the best 100m I did in 1:15 according to the intervals, and 1:01 would be very fast for me at this moment :) How does Garmin calculate this? It looks like it searches for the best four 25m times in the training and sums them to a best 100m tempo. ciq.forums.garmin.com/.../1438575.jpg