Your friend was absolutely correct.
The HWx7 do not have a real anti bear-trap device, just a bit of bent tin that blocks the trigger mechanism when the lever is down. If this is stuck, distorted, missing, hasn't been fitted correctly by a bodger... then it is possible that it may not work.
If the sear engagement on the trigger has also been adjusted to a dangerous level, or some other fault has occured, or worse still you touch the trigger yourself, then the rifle could go off with your thumb in the loading port.
This will remove the first joint of your thumb, guaranteed.
So always hold on to that underlever whilst loading.
Chinese copies of this mechanism have a reputation for this.
Air Arms saw the stupidity of the Weihrauch design and sorted it when they copied it for the TX range. Hence the big spring loaded ratchet that locks into the sliding breech as it is opened. It would take a lot of things to go wrong for that to fail.
Break barrels are a lot safer in that if it all goes wrong you will be smacked on the forehead by the barrel, which will also probably bend upwards and break the stock. But you will still have your thumb.