It was more likely dropped at some point.
If it was over tightening, it would start at the bolt hole.
I just installed a two piece toto drake. I filled the tank
2 test flushes and a crack appeared on left hand side of the tank.
If I over tightened I would think the crack would be the bottom tank bolts not the side.
Am I a dreamer thinking it might be defective? If not I'll man up and buy a replacement and chalk it up to a teaching moment.
And while good, Toto Drake tank QC isn't perfect. I got a bad one a few years ago that was somewhat twisted. It wasn't obvious until I tried to put its matching lid on and it rocked. A few measurements later I concluded the tank was somewhat diamond shaped rather than square. The other two tanks I installed, and the replacement were square on. The twisted tank worked fine, no leaks, but I wanted a flush tank lid that didn't rock.
Take it back where you bought it. THEY are the ones who have to decide if it was defective, not YOU or US.
Licensed residential and commercial plumber