IT MAKES NO SENSE

Hot is per-stream. It just means it has more upvotes in a shorter time than the other stuff in that stream.

In what stream?

any stream i guess, idk

What stream did you get hot in?

It only determines by high amount of views, upvotes, and comments.

Yeah but someone big makes a meme that gets THOUSANDS of views and upvotes and it gets in hot, and then someone small makes a meme that gets 34 views and 4 upvotes and it gets in hot. So i really don't understand this...

That is because if something has 1000 uovotes but it's been 10 years, that is little. It is how many per, not how much. Time also comes into factor because you might see the same meme for years, making imgflip kinda suck cuz u see the same thing u saw years ago.

I've heard that it is determined by a combination of views, upvotes, and downvotes. (I've heard downvotes affect relevance)

then what's the point of downvotes?

To make it not show up as much

It says that Hot is "a combo of upvotes and recency." I guess if you post it in a rarely used stream, it won't get a whole lot of upvotes and it'll just be in Hot along with all the others.