Is it true that if a gerund can be replaced by a noun, the 'gerund' in question is not a present participle?

Take this sentence for instance: We began shouting at the top of our lungs for the bus to stop.

Since the phrase in question ‘shouting at the top of our lungs for the bus to stop’ cannot be replaced with a noun, the mentioned phrase definitely functions as a gerund.

Is this rule correct all the time?