You'd be surprised at how many of those things you think are random would actually emerge as a pattern in long enough purchase history data.

For example, it might be that there's a seasonality to your being in the mood. Or other things you'd have brought a week before, etc.

Over a decade ago a model looking only at purchase history for Target was able to tell a teenage girl was pregnant before her family knew just by things like switching from scented candles to unscented.

There's more modeled in that data than simply what's on the receipt.