if (cond1){
   if (cond2){
     if (cond3){

Is nested because you have conditions evaluated within other conditions, that is, dependent on previous conditions. If you want to be literal about it, the scope of cond2 in the second case is literally nested in the scope of cond1. This is not true in the first form. where the else part is optional. And you have effectively nested an if into the else part of the outer if else, even if the formatting (and maybe semantics) suggests it differently. But in fact it boils down to the exact definition of “nested if”, and I do not think there is a generally accepted one This is an if statement:

if (condition1) {
    // ...
}

This is a nested if statement:

if (condition1) {
    // ...
    if (condition2) {
        // ...
    }
    // ...
}

This is an if-else statement:

if (condition1) {
    // ...
} else {
    // ...
}

This is a chained if-else statement:

if (condition1) {
    // ...
} else if (condition2) {
    // ...
}