I believe LarBrd33 said there is a better chance that the Celtics pick 6th and not 5th is because mathematically they do.
5th is 23.7.%.
6th is 34.2 %.
They also have around a 33% chance of getting a top 3 pick.
That's one way to look at the odds. Certainly the 6th pick is the highest probability slot. So it has a greater likelihood of happening than any of the other 7 possible outcomes.
But another way to look at it is the probability of picking 'at least' as high as each possible slot.
1st overall: 10.3%
2nd or higher: 21.4%
3rd or higher: 33.4%
4th or higher: 33.4% (can't pick 4th so this is really odds of top-3)
5th or higher: 57.1%
6th or higher: 91.3%
7th or higher: 99.7%
8th or higher: 100%
So, actually the odds are a little bit in favor of picking
before the 6th (57.1%).
Edit: clarified a bit.