I find it difficult to agree that its because Prashant got the easier questions wrong because you dont get a pre-decided set of questions with random difficulty. I dont think GMAT has a concept of easier/difficult questions, instead it rates you after your answer to each question. Each time it gets an answer from you it re-adjusts its rating. In the beginning, it will do more drastic re-adjusting because it has no idea, but towards the middle, it could give you a second chance. This is what I observed from my
MGMAT tests, but GMAT could be different.
Yes, making alot of mistakes in the 1st 10 doesn't mean that its the end of the world (or a Q50), but it must have brought down his rating and he had to spend more time bringing it back up. In your case, after 5-6-7, it is possible that the score went down to say something like a Q44 and the next 11 consecutive correct answers brought you to Q50 level and hovered there till the end. The examples of the ratings I gave is just speculation.
Again, I am no expert but this is what I noticed from
MGMAT analysis. I will post a couple of them.
Ultimately, such analysis is not of much use since you never try to make mistakes, it just happens and you cant help it if it happens in the 1st 10 or last. I used it to just manage the time, in case the test becomes difficult