Yes, the LED signal is pretty random sorry! Basically it will react when a bit of MIDI traffic goes through but it can’t be controlled to send a particular data type, at least not without a multi-chip decoder circuit (or a microcontroller!).
A suggestion: you could remove one or more resistors (10k, R8/11/12, blue/green/red LED) to reduce the chaos, or play with a different RC constant (C6/R15; high frequency, C3/R14; low frequency).
