lumpectomy
Cabin crew as a group have shown over the years a higher tendency to cancers, especially breast cancer, so I would think it's not the having had surgery that's their concern, but the fact that since you have already had lumps (benign or not) that you may develop them again. It's all about medical insurance and risk.
Cancer treatments are very expensive for expats now, they are no longer free in the UAE except for nationals.
You did the right thing though, had you not mentioned it, then developed a problem nd it came out later that you didn't report it in the medicals, you would be dismissed without appeal.