Does anyone know anything about M. Meyniel? According to zbMath, he published precisely one mathematics paper, in which he gave a sufficient condition for hamiltonicity of digraphs:
"Une condition suffisante d'existence d'un circuit hamiltonien dans un graphe oriente" (JCTB 14 (1973), 137–147).
In that paper, he was listed with an address but no affiliation. The address was 13, rue Poirier de Narçay, Paris 14ᵉ, which appears to be an apartment above a game store for what it is worth.
I assume that M. Meyniel is distinct from Henri Meyniel of Meyniel graphs and Meyniel's conjecture. That said, the paper "Sufficient conditions for a digraph to be Hamiltonian" (J. Graph Th. 22 (1996) 181–187) is dedicated to the memory of Henri Meyniel and lists Henri Meyniel as the author of M. Meyniel's paper (item [15] in the bibliography).