There’s no way to know about any reduction or ‘bottleneck’, that’s merest speculation. A volcano is a pimple on the planet’s derriere’ compared with a bolide. (nyah nyah) ;’)
A boloid can do much more harm if big enough. The Chesapeake meteor of 34 million years ago left a crater about 60 miles in diameter and resulted in a number of extinctions. However, Toba left a crater 18 miles by 65 miles, and that is a rather large carbuncle not just a pimple. The “speculation” is based on some detailed DNA analysis not just speculation, although I have also heard that it may have been something at least 125,000 years ago that caused the “bottleneck”.