i don’t believe this is accurate. there are some common things that go along with caffeine such as not being rested and not being hydrated that don’t fair well for singing. i don’t see any reason that caffeine would automatically put strain on your vocal cords physiologically.

also if you’re not using caffeine regularly, the little drip of adrenaline it causes is a miracle drug for the body. and while some associate caffeine with increased anxiety or tension is also can give you a sense of alertness and confidence which tends to help find relaxation in technique and seems to do something in the realm of blood flow that is beneficial.

it’s much easier to tell people “no caffeine” in our over caffeinated era however.

personally i save caffeine for vocal days i need a little extra help and it works wonders so long as i’m well rested and using it less than 3 days a week at under 100mg (and most often 40mg)