This workout claims to burn 1,000 calories

I love finding new workouts on pinterest.  The other day I came across a workout that claims to burn 1,000 calories.  Sounds to good to be true, right?  I decided to put it to the test.  The workout goes like this:
Starts with a 10 minute warm up doing jog/sprint intervals.  Jog 1 minute, sprint 1 minute, repeat for 10 minutes.
100 Jumping jacks
100 Mountain climbers
100 Crunches
50 Squats
50 Burpees-Whoa
5 Minutes of jumping rope
5 Minutes high knees
Cool down for 10 minutes with jog/walk intervals.  Jog 1 minute, walk 1 minute, repeat for 10 minutes.
 
 Though the workout is definitely challenging, I didn't even come close to burning 1,000 calories.  This took me 44:03 minutes to complete and my fitbit totaled only 284 calories burned.  All in all it was a great workout, and it did get my heart rate up.  I didn't really expect to burn 1,000 calories, but it would have been nice.  Where are they getting these numbers anyways?