I said 160 bpm 32nds because that was what his metronome was set to!
yep you are right, 160 bpm 32nds = 320 BPM 16ths. the only reason for using the higher tempos is 2 fold:
first: boasting 'yeah thats right I can play double bass at 240 bpm yeah yeah' sounds soooo much cooler than 'I can play double bass at 120!'
actually thats just a bit of a joke the REAL reasons are this:
you can play 16ths at 235 BPM, you can't play 32nds at 117.5 BPM (okay technically you can, but no one does)
the other reason is score writing, when you use lower tempos, and write 32nds, thats a lot of notes per bar that you have to fit into one bar, and it gets VERY messy VERY quickly, so you use a double tempo, and halve the number of notes per bar, which is much easier to read and follow.