The winning criteria are mentioned in the pist where the winners are announced:
Points of all the tasks. In Lesson 2 the total of task 2 + task 3 was calculated to find the 12 best. Next the comments of these 12 were checked to see what they looked like in average (if a response was received was not taken into account). The result is the outcome of the 5 winners.

From lesson 3 on the points given + comments but also using the right hashtags, posting in the right community and title will be part of the criteria because if this is ignored a higher score can still be achieved.