This is unnecessarily pedantic. An exponential back off algorithm has a 100% chance of increasing the delay, that's the whole point. Nowhere other than pure mathematics would I see the phrase "exponentially" and even consider a <1 exponent.
Experience suggests that most of the time when people say exponentially they mean an exponent greater than 1, but I have been surprised by what people have meant before so I personally wouldn't say that probability is greater than 90%. That's what I meant in more detail.