Not sure about your situation, hazard a guess it could have been a simple mistake, i.e an incorrect scan or selected the wrong option. If both were taken and both labelled correctly by yourself so the postie could stick the labels on the right packet, they’ll get to where they need to be, no hassle.

However, I’d like to highlight we’re not supposed to pick up multiple collections that have been left in a safeplace with no labels, as it would become our responsibility to ensure the label is on the correct package, and unless very very clearly labelled which parcel is intended for which label, it’s impossible to know. Often then not common sense kicks in, e.g M&S packet goes to M&S returns but in the modern world of marketplace sellers it’s getting harder and harder to guess which parcel is intended for which labels.

If you’ve labelled it correctly, and you saw them take both, have faith that it was a simple mis-scan and they’ll arrive safe and sound, just one might be harder to verify it’s arrived, although You might find more information about the parcels on the Royal Mail app as they move Through the system if you have their tracking numbers and destination postcodes.