Paul's answer probably sums it up, but for the heck of it, I'll allow myself to let my fantasy run amok ... did you maybe see any ladybird "livestock" on/in the dung?
Many other invertebrates will use dung as breeding chambers for their offspring; for example the Lesser Earwig Labia minor
is often associated with horse dung, but there must be numerous others. I assume none of these would usually be "listed" as prey for Coc.sep.
(or other lady beetles for that matter) but I'm fairly sure the ladybirds are not quite as picky as literature tends to suggest.
Last year, when aphids were at an all time low (or so it seemed), I found a bunch of different species all conspicuously gathering on one particular plant of Tansy (I think - no good with plants). I'm quite certain they were all hunting for - or as a matter of fact already lunching on - the larvae of something like Rhopalomyia tanaceticola
, that normally causes the little galls in the flower heads on Tansy:
Pretty sure this specific menu is not listed for any of those, so it wouldn't surprise me if a 7-spot would find something brunch-worthy on pony dung either ?