You wrote "I had the idea ..." and then linked the paper.
Ha, ha. I guess there's an ambiguity in the meaning of "I had the idea that". Or for that matter, "my idea is that...". It might mean that I am the originator of the idea. Or it might mean (which is does in this case) that it's the idea (belief, notion) that is currently in my head. My thoughts are the thoughts that are currently in my brain, whether or not they are original with me.
Discussion of non-locality of string theory goes back to
Emil Martinec, "Strings and Causality" (pdf) in L. Baulieu, V. Dotsenko, V. Kazakov, P. Windey (eds.) "Quantum Field Theory and String Theory" , NATO ASI Series B: Physics Vol. 328 (1995)
An in-depth discussion of causality of the string scattering S-matrix via open string field theory is in
Theodore Erler, David Gross, Locality, "Causality, and an Initial Value Formulation for Open String Field Theory" (arXiv:hep-th/0406199)
This rediscovered some facts that had earlier been noticed in
M. Maeno, "Canonical quantization of Witten’s string field theory using midpoint light-cone time", Phys. Rev. D43 no. 12 (1991).
See also nLab: causal locality -- In S-matrix theories and string theory, and see the string theory FAQ entry Is string theory causal, given that it is not local on the string scale?
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