Sounds like int tempo.
What were the rest times? This is one tempo workout I use with my soccer girls, except much more! We work up to 6-7 sets, with about 35 sec between and 1:15 between sets.
You know what, I’ll spy on their workout real good next time. I don’t think what they do is very complicated or much of a secret. I’ll count reps, distances and rest intervals and let you know.
I can say that 300m in 46 seconds off fairly short breaks is nothing to sneeze at in 100 degree heat, that’s for sure!