Celtics soured on Markelle Fultz due to lack of explosiveness in workout?

The Boston Celtics seemed to do a quick 180 on top prospect Markelle Fultz, and now we have may have a bit of an idea why.
According to what ESPN’s Michael Eaves tweeted on Sunday, some members of the Celtics organization were not impressed by Fultz’s workout and pointed to a perceived lack of explosiveness on the part of the former Washington star.
Received some surprising info on Markelle Fultz and the #Celtics today. Some within the organization were not impressed with his workout.
— Michael Eaves (@michaeleaves) June 18, 2017
The most glaring critique was that he was not as explosive as they expected/hoped. Afterwards, team felt as if he was NOT the best prospect. https://t.co/83wM5JINWl
— Michael Eaves (@michaeleaves) June 18, 2017
Fultz seemed signed, sealed, and delivered to Boston at No. 1 overall for months. Initially, he scheduled a workout with only the Celtics. But Boston abruptly agreed to a blockbuster deal with the Philadelphia 76ers on Saturday, swapping the top pick for the No. 3 selection and an additional first-rounder.
It’s hard to believe that a single workout was enough to change the Celtics’ mind on Fultz, so there may be some rationalizing for their fanbase in play here. But given the sudden turn of events, this serves as an explanation that will probably suffice, at least for now.