All this is documented in Meijer's actual paper though? (Your mouse is a database) as well as his aformentioned talk (duality and the end of reactive).

He for sure invented observables (as we know it and as the mathematically dual of enumerables) - that doesn't mean it was the first ever reactive system or the concept of data being dependent of other data.

If I remember correctly he also explicitly talks abut Conal FRP and notations in https://www.youtube.com/watch?v=pOl4E8x3fmw if interested