How did they wire a yard light with one switch in the house and one switch in the barn using two power soursces

Pretty hard to do without a switching relay and diodes to prevent backfeed. Hard to believe that was done. Sure it's not 3 way switches?

So, let's say they did...
does it work? and do you want to change something?

Like they say, if it aint broke, don't fix it?

Take a look at the switch handles, do they have "On" and "Off" on the levers?