I used it for all of my chins with no issues. Hay is a product of nature. It is not a man made creation, it will have flaws. They use huge equipment to process it. Fields get weeds, bugs, frogs and more. I've heard of people tossing whole expensive bags because they found a cricket leg...
Here a standlee bale runs about $13.99 for a 45# bale... not a huge loss if it has bad chunks you have to toss. I don't see any black mold on that, it's a type of weeds that's common in hay fields here, when it dries out it looks like that. Hay gets sun bleached, if it rains it turns brown, doesn't mean it's bad, just different colored, no different to an apple that gets cut and set our for a while, turns brown. Once I found a wad of baling twine in the middle of a bale, I just picked it out and tossed it. It's not like they can personally look through every bale, they can't stop and get out if they see a weed on the ground, etc. they'd be there all day!
I'm amazed at how great most commercial hay looks that isn't dyed. We put up hay every year and have my whole life. It's a delicate dance with nature and equipment. Bailing alfalfa first thing in the morning so you have enough moisture so they leaves don't drop out, but not too wet that it molds. You get rain while it's down, it's brown, lost it's color. Wind will blow your rows and you'll have to go re-rake.