I personally believe it is the second,
I have seen translations that say one should also not derive benefit from it, though it seems likely this conclusion was arrived at through gematria. It also looks likely that a large number of the rules are disciplinary, to make sure one does not accidentally break the underlying rule.
Another explanation that I came across is that at the time there were pagans that believed by boiling a young goat in its mother’s milk and spreading the mixture around a field, this would cause the gods to be pleased and may give them a good harvest for that year.