What makes a triathlon tyre different??

I would imagine that any low rolling resistance light weight tyre would do for triathlon use... Do enlighten me.

[that'd be 'tire' in American]

I think it's purely marketing. It's not like the tire swims or runs.

As caloso said it's marketing. Some people's triathlon tires are very race specific, like you guessed. Others are puncture resistant.

No manufacturer calls a "triathlon" tire the same thing.