62.5 micron multimode 1000BASE SX has a range of 220m
50 micron multimode 1000BASE SX has a range of 550m
9 micron singlemode 1000BASE LX has a range of 5000m

they would have used fibre to electrically isolate the buildings. That is, you could end up with a potential difference between the buildings which is enough to fry the network gear. This would be even worse if you had a lightning strike nearby.