My guess is that the person you sold to may have only purchase hair during the time when hanks were "accidentally" fuller, or more recently.
The majority of time time that I was purchasing hair from DH (2010 throug end of 2012) hanks were pretty uniform, and pretty large. Then at some point they all got immediately and drastically smaller. The response from dollyhair was that they were always supposed to be smaller, we'd just been getting larger hanks for years by accident... or something. The owner then set a more standard size somewhere between the larger size we had been getting and the smaller size.
So anyway! Yes, way older hanks (pre 2010 anyway, I don't know an exact time frame but this is from my experience) were smaller than the 'accidentally' larger hanks sold more recently. I've purchased several unopened hanks from customizers old stashes that were smaller than others I have received more recently, but that's the norm.
In other words:
Time period A: small hanks (oldest)
Time Period B: large hanks (older, but within past 4 years)
Time period C: small hanks (a few months in 2012/2013)
Time period D: medium hanks (current)
Hope that makes sense.