There are loads of different reasons for guys to have scars similar to DI. Lots of cisgender men get a similar surgery to correct gynecomastia, and their scars are very similar if not identical to the DI. Obviously it's one thing if you just don't like the aesthetics of the DI. But the scars alone aren't going to out you. There are plenty of reasons for scars like that: mastectomy, gynecomastia, double lung transplant, pectus excavatum, collapsed lung, tumor/cyst removal, etc.
Or you could make up something cool like "epic bar fight" or "bear attack".
I know a lot of people are dead set on certain procedures, but I've always had the view that I'm not the professional in the situation. I let my surgeon choose what she wanted to do, and I think I will have better results because of her choice, though it wouldn't have been mine.