A smart birdy landed on my shoulder this morning and whispered some sage information to me.
It turns out that malt contains a precursor to this ester. Its an alkyl aldehyde called heptanal. There are journal articles that show that the heptanal content of barley is dependent upon the cultivar. I would also have to assume that it's concentration might change during malting and kilning. I see that the Kovats retention index for that compound is fairly low, so it is likely to be driven off to some degree during kilning. Paler malts are therefore more likely to contain this precursor.
Heptanal is converted to ethyl heptanoate through the metabolic action of yeast. Ale yeasts are most prone to this metabolic action. Interestingly, this Helles I'm referring to was fermented with US-05 at 52F. So it is possible that this is the source of that ester in my beer.