So yes, in fact the LFOTool Plugin is outside the Ableton Effect Rack, so the Macros in the effect rack are not triggering LFOTool, I should have seen this the first time.
- When you click on the 2nd icon on the right side of the rack ( 1 - highlighted in green ) it will expand the rack and reveal the chain(s).
- Clicking on the 3rd icon ( 2 - highlighted in blue ) reveals the devices contained in the rack, in this case CS is using FabFilter Volcano 2 plugin and that's what the Macros are linked to and if you click on the "Map" button at the top of the effect rack, it will reveal the Macro Mappings in Live's inspector ( everything 3 - highlighted in Yellow ).
So that's what this filtering rack is doing, I don't know if you have Volcano 2 plugin to check this out, if you don't you could try to use another filter plugin or Ableton's native "Auto Filter" to try to replicate.
So that's how the filters are set on those Side-Chain effects return tracks in Live. Now to trigger either the "A-Heavy Sidechain" or "B-Soft Sidechain" CS is using another Effect Rack inside the "SIDECHAIN TRIGGER" track as you mentioned. Again, if you expand the chains, you can see that he's using 2 different chains with an "External Instrument" device on each one linked to the LFOTools plugins either on return Track A or B and the automation lines are controlling which one is triggered. Since all effects chain are processed from Left to Right before reaching the output, in each case it will then go 1st to LFOTool and then the following Effect Rack on return A or B.
So that's the principle, again I haven't watched the tutorial myself, so it's hard to go into details and it's quite a complex routing, the benefit is that he's able to control different sidechains effects with automation.
Hope this helps to better understand the principle & routing, but yes, its quite an advance way to do it, so it might take some trial & error to replicate.