ABCDEF is 6 digits, so zero through 999,999, one million possibilities. Not 100 thousand.
I purposely neglected cars having less than 100,000 miles because we know the number has 6 digits (not 5). And I purposely neglected cars with over 200,000 miles because there are much less of them. This was just to get a round number (100,000). Of course you could stretch the range to be from 100,000 to 300,000 instead, giving a range of 200,000 possibilities. But frankly, the probability of a car having anywhere between 300,000 and 999,999 miles is negligeable IMO.
A more accurate model with 100,000 possibilities is to consider that a weight curve for car mileage has a peak at around 178,000 miles. So sticking with 100,000 possibilities around 178,000 is close enough for me (a bell curve centered on 178,000 ± 50,000).
Either way, 100,000 possibilities is a round number with ok accuracy. If you want to consider a wider range, you'd have to account for weights (how many cars in the US for each value of mileage). Not sure it's worth it for this thread.
Basically, imagine a bell curve centered on 178,000 miles, and trim off the tails. Then, square it off to make a rectangle centered on 178,000. Now you have an equal probability for each possibility between 128,000 and 238,000 miles. Chances are the powerball number is in there, and you have 1 chance in 100,000 to get it.