Its an example of sub-literate content creators and nothing more.

You could have told him… is in the past. You didn’t tell him. You could tell him.. is in the present. You still have the option to tell him.

This kind of question deals with very subtle differences in meaning that most native speakers are not aware of. People often use these constructions in ways that don’t technically express exactly what they are trying to say, but that doesn’t matter to them or to the people they are talking with. As a student, you don’t really need to be concerned with them unless you’re a very advanced student or are studying for a very sophisticated exam.

You could tell him if you want to. (Now) You could tell him if you wanted to. (Now) You could have told him if you had wanted to. (In the past) You could have told him if you wanted to. (In the past) The two pairs have similar meanings despite using different tenses for ‘want’.

Let's compare these two: You could tell him if you want. You could tell him if you wanted. Both sentences are timeless. They don't necessarily occur (although they could if context is given) in the frame of a past, present, or future. The only difference is that the second implies that "it appears that you don't want to tell him". Now let's compare these two: You could have told him if you wanted. You could have told him if you had wanted. The first says the needed conversation would now be over and done if he wanted it that way. The implication is that he does not want it that way. The second says the needed conversation would now be over and done if he had wanted it that way. This implies that he did not want it that way, but leaves open the possibility that he might now want it that way.