Well, from my little experience, I might be right, I might be wrong, if I am wrong, I am open for correction..

But I actually think that Bitcoin halving have little to nothing to do with Bitcoin mining difficulty, this i think because, the difficulty can go up or come down on this own, the factors driving the difficulty up or down i am not sure of, but i think it has something to do with number of miners online mining bitcoin at a particular time, that is to say that, when there are a lot of miners mining bitcoin, the mining difficulty increases, and when there are less miners , the difficulty reduced, this increase and decrease i think also have something to do with the total hashrate or whatever its called..

The takeaway here is that, i believe halving has very little to nothing to do with increased or decreased mining difficulty since this aspect of bitcoin also goes up and comes down on its own just like the price of bitcoin.