But is it a lie, or is it an error?
There’s a big difference between the two.
Except that Trump is saying that “a lot of people must have died” because it was a major river crossing and that is where that things like that logically went down according to him. Reading between the lines what he really means it that this must have been a prime battle site because it occurred in a place that now happens to be the location of his golf course.
You're right. We should give him the benefit of the doubt and assume it's an error. Now that it's been brought to Trump's attention I'm sure he will rush to correct it.