Not sure it's different tobbacco at all, just a "Cuban Sandwich" construction.
In a long filler cigar, each leaf is the length of the cigar, these are your typical premiums.
In a short filler cigar, leaves are chopped up and used to fill the cigar, these are your typical machine made cigars.
A Cuban sandwich is made with several long leaves and some scraps from making long filler cigars "sandwiched" in between the long leaves. These scraps are not shredded the way short filler cigars are made, they just are not full length or "Medium" filler.
They are a bit cheaper because they use the tobacco more efficently than long filler cigars, down side is you may get the odd one where the draw isn't as good as you would have with a long filler cigar. I keep my main humi at 70%, but find the Tat White smokes better if you dry them out a bit before you smoke them, or keep your humi at 65%. I keep a desk top humi at 65% for what I'm gonna smoke soon.