If you went to a good friends house and had a delicious meat meal only to discover it was human meat how would you react?

I would be pissed at the risk of prion disease.

I'm reminded of the story of Liu Bei in Romance of the Three Kingdoms, when he was driven out of Xiao Pei, and he didn't know the fate of his sworn brothers or even his wife and children. He fled with a few retainers and eventually their supplies ran out, so they have to go into a village to ask for help from the villager there.

Liu Bei had no better plan to propose, and the two men directed their way to Xuchang, choosing by-roads rather than highways. When their small supplies ran out, they entered a village to beg. But when the people of any place heard that Liu Bei of Yuzhou was the man who needed help, they vied with each other in offering all that was required.

One day they sought shelter at a house whence a youth came out and made a low obeisance. They asked his name and he gave it as Liu An, of a well known family of hunters. Hearing who the visitor was, the hunter wished to lay before him a dish of game, but though he sought for a long time, nothing could be found for the table. So Liu An came home, killed his wife and prepared a portion for his guest.

While eating Liu Bei asked, "What flesh is it?" Liu An told him: "Wolf."

Liu Bei knew no better and ate his fill. Next day at daylight, just as Liu Bei was leaving, he went to the stables in the rear to get his horse and passing through the kitchen; he saw the dead body of a woman lying on the table. The flesh of one arm had been cut away. Quite startled he asked what this meant, and then he knew what he had eaten the night before. He was deeply sorry at this proof of his host's regard and the tears rained down as he mounted his steed at the gate.

In plain language, the hunter did not have good meat to offer to Liu Bei for a meal, so he murdered his wife and fed that to him, telling him it was wolf. When Liu Bei saw his murdered wife the next morning, he realized what he had eaten the night before, and cried because he was moved by the hunter's regard for him, that he would go that far to give him a good meal.

Didn't happen in real life (not that I know, anyway), but it's an interesting story.

This is how I would respond

It tastes like pork.

Sources tell me.

https://youtu.be/cJQqgxz863w?t=15s

Depends.
How did they get the meat?

If they murdered someone, I'd be pissed and call the cops.
If they got it without murder, then I could deal with that.

I'll eat any animal that I didn't have a personal relationship with.
I would never eat my cat. But I would eat yours. And I probably wouldn't eat you, but I'd eat your sibling if they were served in a non-homicidal way.

Braaains.