I have a friend that has whacked a lot more beasts than I have. He also has whacked more beasts relative to bushes than I have.

His numbers are (aproximatley): 157,000 bushes to 22,000 beasts
My numbers are (aproximatley): 165,000 bushes to 18,000 beasts

any theories about the difference in game play that could create this difference?

yes Halloween beasts were beasts even though they only dropped one item.
randomness is the cause of your friends difference, well within possibility.
but they could whack forever in the Tomb of the Restless I suppose.

my own numbers:
Total Bushes Whacked 1,219,361
Total Monsters Whacked 129,733

or while at Max (which is something like 350 days out of 450 days of my playing):
Bushes Whacked At Max Level 1,013,367
Monsters Whacked At Max Level 107,407

roughly 9:1 either way. Perhaps some specific areas might have lower ratios.

perhaps 500K of those were Level 1 Bushes and Level 1&2 Beasts in that very first square, yes there are no Level 2 Bushes in The Bushy Woods. These were over perhaps the last couple months while working on 2 Achievements, 1 Mill Bushes and 1 Mill Bushes at Max. Now to only get to 200K Beasts... UGG only 65% of the way there.