The ancient Greek people distinguished intercourse from orgasm.
Isn't the idiom distinguish X from Y correct?
Does the past tense change things?
Tense is not the issue here.
The sentence should read "...distinguished between intercourse and orgasm.".
First, because intercourse and orgasm are closely related.
Second, because we have only two things to distinguish (between).
Compare: "The Brown twins are so similar that it is impossible to distinguish between them.".
Here it means to perceive or point a difference between
The idiom "distinguish x from y" is correct when you want to differentiate/characterize an item from some others.
Compare: "Dogs can distinguish the trailed smell from all others."; "You will distinguish him from the crowd by a red hat.".
Here it means to discern
Basically, these two idioms have different meaning.
If I answered your question with this post, use the motivating power of kudos!