What were your actual temps at night though? I get the slab came out nice but 38 during the day can drop to 25 overnight and that's where guys get burned. Honestly I've seen cold pours go great and I've seen them crack all to hell, and the difference was almost always cure time and whether someone stayed on top of the blankets. Your lead wasn't totally wrong either, he was probably talking about the old days before heated mixes and good blankets were easy to get. Tbh I'd rather pour in the cold than in 95 degree heat where the mud sets up on you before you can even get a finish on it.

My buddy moved his to the sliding door and same thing.

Isn't it funny how the fix for one thing always causes some other problem down the line? Same thing happens with phone chargers, you wrap them tight and the cord quits working a few months later. Tight just always feels faster in the moment, then you pay for it later.