The gear down indication on the EMB 135/145 is on the EICAS with an additional backup system on an RMU sub menu page. There is no mechanical indicator and now way to tell from the cabin if the gear is down and locked.
A landing gear disagree audio/visual warning is generated if the gear is not in the selected position 20 seconds after the gear command.
If the gear was not indicating down there would have been a mode 4 'too low gear' gpws warning below 500ft.
Additionally, a landing gear voice warning 'Landing Gear, landing Gear' is annuniciated below 1200 ft RA if land flap is selected and the gear isn't down.
It can be seen that there are plenty of warnings to prevent a gear up landing - a very strange incident indeed, and one I look forward to seing the technical reasons for.