Another question on expansion of the universe.

I can't wrap my head around this generalized statement. "If we were to detect deviations from flatness in the observable universe, then it would provide evidence against inflation. "

What does that mean? to me expansion/inflation would suggest a non flat observable universe. I can't wrap my mind around a concept that to me makes it sound like the expansion is linear vs the "loaf of bread" concept where space is increasing regardless.