Any one of 3 things, or a combination of 2 or even all 3. Possibly even a 4th.
1) Cooked and served in the Balti pan.
2) Containing the main "meat" ingredient plus vegetables all cooked together. (? Vegetarian Balti)
3) Using the "Balti" spices.
And possibly the Champagne argument,
4) Birmingham only. Or maybe Baltistan as well. ;D
There are other minor contributors.
Must be eaten with bread and no utensils.
Must be eaten outdoors squatting by an open fire.
Can only be judged as a "Real Balti" by someone over the age of 65 who actually had one in the 1970's in the Balti Triangle and swears that they were better than any of the stuff sold today anywhere in the world. I remember when Weston's Wagon Wheels were this big.
https://www.appliancecity.co.uk/news/updates/is-our-chocolate-getting-smaller/Ooops.

That doesn't work at all. Oh well, you know what I mean.
Of course you could just cook one as described in one of the Authentic Balti cookbooks and think your eating one. Nobody will ever know. That's what I do.
I like MR'S recipes. I'll give this one a go.