That's not obvious from the comment and logically inconsistent with parts of it; if the trace between the cells is small it would act as an auxiliary fuse, and there is that balancing resistor (whose value I can't read because whoever drew that schematic didn't bother repositioning overlapping labels.) I'm also a bit confused about the 2 polyfuses.

That said you're right and I was focusing a bit too much on my reading/interpretation of the GGP post. I'm not sure I've ever seen a 1S2P LiIon configuration with individually user swappable cells. In the 2-cell design I did, I specifically decided to go for 2S1P and have the balancing circuit, to avoid this exact issue. It does have the downside that you need both cells, the WHY design works with only one populated... (which is what I'd recommend doing in any case.)

[ed.: the balancing resistor seems to be 200Ω. The polyfuses are 15mΩ. So I guess it's designed to trip one or both polyfuses if the cells are imbalanced. That's an... "odd"... design.]