Here is a better pictureIf your talking about the white line I don't think so. That looks like he either rubbed against something white or he scraped it. Just keep an eye on it. If you think it starts looking like it's getting worse, try some antifungal cream on it and put him in dry dock for a while. Still giving him water to go into but making it very shallow.
Thank youOkay, now I see better what your talking about. Yes, it could be. I would use some antifungal cream on it. However, that's how I would treat a tortoise. Maybe @Markw84 can help