It's more that the mushrooms and chocolate synergize in the body metabolically. Cacao is said to be a heart opening plant medicine, and in combination with mushrooms, which (IMVHO) are more mind expanding than heart opening (although the latter can be a side effect of consuming mushrooms), the effect is a bit more profound with a different kind of depth to it. There are molecular mechanisms at play here (the serotonergic receptor system as well as olfactory receptor system), so there is actual interplay at that level influencing these phyiscal and psychological effects.