DB's Average CMC Flawed?

I noticed it on this deck of mine (https://deckbox.org/sets/3074479).

There's a bar graph that has the individual card CMC (0-6 and 7+) on the x-axis and the frequency on the y-axis.  I have found, when I've checked, that this chart is accurate.  However, using the above deck as the example, the Avg. CMC figure to the right of the chart doesn't pencil out.  I don't think my method or my calculations are wrong.  Wondering if anyone else has noticed this or if there's something I'm not considering.

12 cards x 1 CMC = 12
8 cards x 2 CMC = 16
15 cards x 3 CMC = 45
1 card x 4 CMC = 4

Total = 77
Total cards = 36

Avg. CMC = 77/36 = 2.14.  But the field shows Avg. CMC for this deck is 2.42.

Almost all of my decks, when I calculate by hand, show a disparity, though nothing systematic (i.e., they're not all higher or all lower).  I don't see any effect from the sideboard, which is sensible.  I have filed a support ticket but have seen no response.