I probably would - but I would pose it as a question -
"That block seems to be facing differently that the other - is it supposed to?"
"The flowers in the fourth border seem to be cut from a 'different place/stripe' than the other borders - had you noticed that?"
"That piece of fabric seems to be reversed from the others - is that a design element? If so, maybe it would look better if you turned over more than one?"
I'm tired of the hearing about the 'humility block' - that just seems arrogant sounding to me. I think most of us make enough unintentional mistakes without having to make a 'humility block.'