It appears from the pictures, like the others stated, that it is a crack. When you have real leather it has imperfections and over time they will show up. ESPECIALLY if someone doesn't keep up the conditioning of the leather (I have been very guilty of this and have a favorite chair with a place just like this on an arm - very visible area).
When you are dealing with genuine leather, "weaknesses" like this will show up over time - which is inherent in it. I always advise buyers when they are looking at genuine leather and "faux" leather that if they want the chair to look pretty much the same in 10 years to go with faux but that it doesn't wear as well and will become saggy and dull looking. The genuine leather will keep it's look but can develop cracks/etc unless maintained (and sometimes even when maintained due to the weight stress from sitting on it which is a heck of alot different than the natural stress points from the cow wearing it!) Kind of like us humans, we develop "character marks" such as wrinkles/spots etc over time.
If it bothers you enough, there are leather repair places out there that can come out and mix up an "epoxy time material" to "glue" the edges back together and you will barely notice it - but it will still be there. If you are going to do that - DO NOT do anything else to the leather at this point so they can get a good grip on the leather without conditioning build up. Or you can wait and do it later.
Thank you! It doesn't really bother me, unless I did it myself 2 days ago when I was moving it. I know that sounds weird.
I like the natural wear and tear (patina) that especially leather gets...I just have a weird mental thing where it drives me nuts when I know that I was the one who damaged something. If someone else did it, I'm fine. (Again, weird I know!)
So do you think that the crack has been there for a while, or could it have been done 2 days ago?
I did put some leather dressing on the chair the day that I got it (and over the crack).
Also, it is right in the middle of the seat back where your back/head would be...so it would probably be the area most prone to wear and tear.