My guess is the parent poster was assuming the concern with liability was if they were charged by someone with a hammer (unprovoked), and you are assuming the concern with liability was based on stopped the robbery - both seem like pretty legitimate readings.

In less populated areas, my experience has been that individuals pretty much have to take responsibility for intervening in things they see - since no one else is around or could be around to do anything in time - or quickly things get out of control in a wider sense. I have property in an area that it’s easily 45 minutes before you could get a police response to a real, active emergency just due to travel time from the station. If you don’t intervene in anything weird, even if it isn’t your property, then the whole area gets a reputation for lawlessness pretty quick and attracts more problems. The attitudes of the local law enforcement generally are friendlier too towards getting more help, as they are well aware of how little they can do without it. They also deal with fewer things like folks itching (or able) to sue, due to it often being poorer areas, and everyone being less up in each other’s faces all the time.

In urban environments, there are often dedicated folks nearby (as in a few minutes response time), and everyone tends to be tenser - and the problems are often less ‘help me, I’m stuck in a ditch’ and more ‘semi-insane and/or drunk people getting in a fight in a public place’, and more people have the resources and/or access to lawyers to make things a nasty mess. So in general it IS better to call in the specialists who are used to dealing with it, and stay out of the mess if you can.