Running an engine at full throttle with a load is one thing, but running at full thottle with no load is probably the easiest way to "blow" a motor. With no load (and no rev limiter), the engine can actually rev well beyond its mechanical limits and spin a rod bearing, throw a rod, etc.

So this could have potentially been 'fatal' for your motor, but it sounds like it survived unscathed. You would know if there was damage by the way that it runs.