The strings should be grounded, via a wire soldered/connected to the anchor of the tail piece or bridge, and as for the PKup cavity ground I am not sure if he means the plate the pkups are attached to, or a central grounding FOR the pickups themselves then wired as one ground wire back to the control cavity to keep less wires in that area. either way he was jumping the ground from the buffer.
As for your wiring, I gave it a shot to follow, but it is a little hard to see, It may be grounding itself on that foil if anything like the pots or unprotected joints/wire ends are touching it. Check your pots to be sure they're wired right. I followed rosebud's so I haven't attempted the Tiger thing yet, but I would re-wire it step by step in your mind, point to point through the schematic. I know you will fix it, everyone has trouble their first time, and my god, you attempted one of the craziest guitar wire's known to human existence! I have heard of experienced Luthier's getting questionable on this particular build... You have done a great job so far....almost there!! -JB
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