I’m guessing you paid for the materials? Easier for the contractor to buy a bunch extra to save him an extra trip when he messes up on one too many tiles.
I recall working with my dad on home-building projects. We could do the math okay. I was always amazed at his carpenters that could use their right-angle measuring things with all of the shorthand calculations on it. That was a real mystery to me - like a slide-rule was!
I have a bunch of right-angle measuring things! I also have a couple slide-rules from when I was young; something we had to learn to use in high school way back then. Carpentry is one of my hobbies, and my being a math major helped with that hobby.
As for the bathroom remodel, I paid the contractors for the labor but I had to buy the materials and supply it to them. I've been remodeling an entire house and needed the extra labor to get the bathroom completed while I focused on other work. Just put the house on the market and am glad it's done. Now I can go back to making furniture for fun.