Offline audio-rate convolution (particularly with shorter impulse responses) has been plausible for a while, but real-time convolution reverb has definitely come into its own over the last ten or fifteen years. Overlap-adding blocks of audio that have been processed in the frequency domain with a low enough latency so as to feel instantaneous is a more recent capability that likely had an influence on this work.

I think the reason they used balloon pops was because that was all they were allowed to use: many heritage or archaeological sites can be nervous about researchers bringing in large loudspeakers and amplifiers, whereas a portable recorder and a bag of balloons can feel a little more harmless. Most acoustics researchers are aware of and use those new techniques whenever it's possible!