Their particular exploit for variant 1, which uses eBPF, only worked on AMD with the eBPF JIT, i.e. it did not work with the eBPF interpreter. But there are many other potential avenues to exploit that variant which have nothing to do with BPF. The result does suggest that it may generally be harder to trigger variant 1 on AMD processors (because they doesn't speculate as much?), but harder ≠ impossible.