As we have seen, the halving did not lead to an immediate price increase. That's no surprise since the event was known years in advance. Investors and the mining industry generally prepare their positions before an event. Indeed, the Bitcoin price did rise prior to the halving. However there is no clear proof that the halving was the reason, since there is an uncountable number of other possible factors that could have influenced the Bitcoin price
There can indeed be an innumerable number of factors (most of them offsetting each other, though), but you still have to explain somehow the almost
four times growth in the Bitcoin price within just a year. Saying that a lot of factors very efficiently and very timely added up to boost the price so high just doesn't cut it. I think it can be readily explained by the collusion of the Chinese miners (actually mining pools) to prop up the Bitcoin price before the halving (by withholding bitcoins they mine)...
If you think there is none, think again, for example, about the block size which is still where it was a year ago