Yes, brown blood is old blood. Perfectly normal. Many women do have this as they start and end their period. good luck
I am not a doctor, but I too have had this problem in the past. I talked to my doctor and I was told that it is old blood that was not expelled from your uterus during your menstral cycle and is now making its way out. It's very common, I was told.
If they did a swab test and it came back negative this is very likely what it is.
If you have anymore concerns about it call your doctor and talk to them about it and I'm sure they can give you more information!