This is right Gaza
It would have been a landing weight restriction as to why things were offloaded. The max landing weight of the Q400 is 28,009kg. If you were nearly full, with lots of bags etc then you could have been close to the max take-off weight of 28,998kg. The trip fuel between MAN & SOU can be as little as 800kg meaning an overweight landing. Factor in SOU's short runway and icing conditions the regulated landing weight could be alot less than 28,009kg. Something has to give, generally it is positioning crew first, followed by bags. They could have offloaded pax, so it isn't all bad. Just one of those things.