Look at it this way a piece of plastic tube is unlikely to do any harm: if a commercial garage had done this they would be unlikely to tell you and you would never know and you would carry on oblivious. It's unlikely to get into the oil ways and the connecting rods and crankshaft are big hefty parts.
Obviously if you are really concerned the only way to recover it is to drop the sump, or if you are lucky it might, although unlikely, come out if you drained the oil.
Looking at both ends of the fishtank airhose, they look quite cleanly cut. I think to snap the hose would require a lot more force than I was using, and leave a jagged edge. So going to assume a bit didn't break off in the sump.
Not sure if my local Honda garage drain oil through the dipstick, or sump drain plug.
My main concern now is the rattle/knocking sound. Hard to pinpoint, seems like from the belts (tensioner needs adjusting maybe?).
rattle/knocking from the front of engine... do these engines have Timing chain tensioner (TCT) issues? kinda sounds like that imo.
any idea what oil was there, and what oil you now have? my thought would be it's the oil. brand of oil was a big 'thing' for the s2000. some would be thinner (so noisier & burns more per miles) than others of the same rating. bit of a minefield tbh as even some of the branded ones were similar to cheaper own brand labels.