in an effort to not do school work I messed around with it and found something weird. It doesn't seem to be a simple case of mashing or dropping x bombs by y time span upon falling. I've found a consistent method to make it work doing buffers which may shed light on how the trick works:
when you fall in the whole and the next screen loads, map buffer. Inventory buffer out of leaving the map, drop a bomb into another inventory buffer. Inventory buffer again and then drop another bomb and it should work (dropping 2 bombs within 2 frames of eachother??).
Very very weird. here's some cluttered chat log with my thoughts
hmm
[7:19:46 AM] Leon P: it seems to be a mashing thing
[7:19:49 AM] Leon P: for interest I'm usin turbo
[7:19:52 AM] Leon P: and hasn't failed once
[7:22:26 AM] Leon P: doesn't seem tied to bomb count
[7:22:40 AM] Leon P: there are times when I drop 4 and it does work and times when I drop 4 and it doesn't
[7:22:53 AM] Leon P: doing it manually
[7:27:50 AM] Leon P: I mashed hella fast and didn't get it
[7:27:53 AM] Leon P: I mashed slower and got it
[7:31:45 AM] Leon P: I'm guessing it's not a sprite or memory overload thing
[7:32:17 AM] Leon P: b/c I've gotten contradictory results by going with bomb dropped amount
[7:32:54 AM] Leon P: and then there's inconsistencies in mash speed that have gotten contradictory results as well, in the few tests I've done
[7:33:45 AM] Leon P: maybe using a bomb on the frame the cutscene is supposed to be loaded cancels it or something? this sounds like something for drenn/tompa/mab
[7:34:36 AM] Leon P: which would explain why using the turbo worked 100% of the time, but at times manual mashing had different outcomes
[7:35:23 AM] Leon P: I don't know about the specifics on how it does work but it feels to me like it is a target frame thing and not just a simple case of mashing. At least that's my guess
[7:36:39 AM] Leon P: so messing around further
[7:36:47 AM] Leon P: it just worked by releasing only 2 bombs using turbo
[7:37:10 AM] Leon P: and doing the same thing in different timings doesn't work
[7:49:16 AM] Leon P: something bugs me though
[7:49:16 AM] Leon P: that turbo works 100%
[7:49:16 AM] Leon P: when turbo isn't 60hz in BGB
[7:49:16 AM] Leon P: so I don't think it's just 1 frame