It's possible to weigh the packs to find the ones with foil cards if you have an accurate scale. It's more likely that these packs are the left overs from fat packs though.
GrolormTheoretically they could be weighing them. However I doubt they will invest the time and energy into this. Plus the last Mtg product I purchased recently was two booster boxes and two fatpacks. Each box contained a expedition land. If they were repackaging and resealing the boxes I doubt I would have pulled them.