Gottschalk is attempting to do two things here:
- Have the left hand maintain a steady eighth-note pulse, which provides the rhythmic foundation for the piece.
- Make the piece look visually impressive to perform by having the left hand leaping around the keyboard and sometimes playing melody notes rather than the right hand.
To that end, the notes labeled 3 and 5 in the question are both left-hand notes, and the notes at 6 are played by right (upper note) and left (lower note). This pattern occurs throughout much of the piece.
The reason for the cross-staff stems on note 3 is to make clear that while the left hand will play the note, it is part of the overall sixteenth-note pattern initiated by the right hand.
Similarly, at "5", the double stems show the two voices, how they fit rhythmically as "pulsed-by-the-left-hand" moments, and two help clarify that the left hand should play the melody's "G" (along with the accompanying voice's "E").
Arguably, one could play the pictured part without the handedness trickery, sacrificing flash but maintaining musical intention. But, I think the musical goals are more effectively (or, at least, more easily) maintained by using Gottschalk's approach — by making the eighth-note stresses more clear.
Below are pictured the same measures from the Schott edition (also on IMSLP).