What they're doing is something like branching off a very old version of master, making changes to file A then trying to merge into the latest version of master

What they're doing is something like branching off a very old version of master, making changes to file A then trying to merge into the latest version of master, which already has a load of changes to file A. They then resolve the conflict by picking "ours", thus ignoring all changes on origin/master in favour of their own old version of master. This doesn't require a --force.