"Since 1863, the British had been trying to force the King to stop selling slaves to the Arab traders who had replaced the Portuguese after 1836. . ."
Is just complete nonsense. There is simply no part of this sentence that is actually correct. Somebody with a very active imagination was at work on this part of the page, apparently. As for the stoppage of "human sacrifices", there were just a few individuals from Britain in the late 19th century who had visited Benin that had suggested this, but nothing like an attempt to "force" the kingdom to stop such executions occurred, nor was this issue even one of the main reasons for British encroachment in the region or on the Benin kingdom. The motives involved were economic/trade-related and the executions were of no great relevance to why the invasion occurred.
Then there is another incorrect sentence:
"This had increased after the Atlantic trade ended as the leaders "supernatural rituals and large-scale human sacrifices to protect the state from further territorial encroachment.""
This sentence cites a page on a random art website which cites no sources and has no stated author, and which does not even seem to realize that the kingdom of Benin (in what is now Nigeria) and the modern Republic of Benin are totally distinct and different places.
This sentence also cites an article containing multiple errors and pieces of misinformation by one Bolaji Aluko, a man who is not even taken seriously in his country of origin. Aluko just pulled together anything that he could, without doing any sort of actual research or investigation to verify what was or was not accurate, from various websites on the internet, and after compiling all of this information - some parts of which contradicted other parts of his article - called it a quick "history lesson". There are in fact at least three already existing scholarly discussions of the subject that this person's supposed "history lesson" is meant to cover (one of which is Graham's easily accessible article), that had already been published decades earlier by actual researchers on the Benin kingdom, and all three of which independently reached quite similar conclusions to one another.
Also, although there is one citation of Graham's article on the page, there is also nothing which explicitly notes that those remains of "sacrifices" that were seen were mostly the remains of executed criminals. Nor does it note that some of the dead that were seen would actually have been some paupers that for whatever reason did not receive a proper burial, and possibly even some people who had died of influenza (there had actually been an influenza outbreak in the area in the early 1890s).
So, yes, the article as it currently is written should be somewhat revised.
Why not? They could've done human sacrifices during the British occupation, that Felix recorded when he was there as a medical assistant.
During the period that the British actually occupied the city there were no sacrifices. The British accounts make no mention of anyone from the city attempting to kill anyone else, whether as a "sacrifice" or for any other reason, after they had successfully occupied the city. There was fighting between the British and the Benin soldiers from when the British landed in the area up until the British reached Benin City and captured it (and there was an attempt by some soldiers remaining in Benin City to fire cannon at the British force that was entering the city, but this was not successful - they were killed by the British soldiers before they could hit anyone), but after they captured the city there were not that many people remaining, there was not any fighting nor any sort of resistance within the city itself*, and the place was under complete British control, so there could not have been such killings anyway. There were just a few nobles and some commoners left within the city after the British occupied it, but not that many people overall at the time of their occupation, and there is no mention by the British of an executioner (or anyone else) from among the populace of the capital killing anyone as the British were entering the city or during their occupation.
*There was however, a resistance force which had gathered some distance outside of the city, in some other towns, which the British defeated by 1899.
Thank you for this paper.