If the break originates out from a little figure 8 / butterfly shape at the centre, it's likely a spontaneous failure due to a nickel sulfide inclusion in the glass, not a thrown object. These failures are expected to occur in 1% of tempered glass sheets over the first 10 years, so on a station renovation with lots of glass a breakage like this is almost guaranteed. There is no immediate urgency in replacing a sheet of shattered tempered laminated glass like this, as it's engineered to work with just fine with only one side of the glass present.
https://failures.wikispaces.com/Glas...ide+Inclusions
Shattering tempered glass by throwing something at it actually is very difficult. I doubt anyone would go to that much effort, but you never know!