The most truthful lie there can be? [duplicate]

I was wondering whether it classes as lying if you tell something that you believe is a lie but is actually true.

Here is an example. Let's say that you have to be 6ft to ride a roller-coaster. You think you are under 6ft and say that you are tall enough but, in fact, you are tall enough. In this example, you haven't given a false statement but you have given what you thought was a false statement as your intention was to lie about your height.

Is there a certain word or phrase for this?

Warning: philosophy; does not necessarily match with all dictionary definitions of untruthful, but certainly with some.

Untruthful truth, also: a lie.

(L1) To lie =_df to make a believed-false statement to another person with the intention that the other person believe that statement to be true.

[...]

According to the untruthfulness condition, lying requires that a person make an untruthful statement, that is, make a statement that she believes to be false. Note that this condition is to be distinguished from the putative necessary condition for lying that the statement that the person makes be false (Grotius 2005, 1209; Krishna 1961, 146). The falsity condition is not a necessary condition for lying according to L1.

[...]

Statements that are untruthful may be true. In Jean-Paul Sartre’s short-story, The Wall, set during the Spanish Civil War, Pablo Ibbieta, a prisoner sentenced to be executed by the Fascists, is interrogated by his guards as to the whereabouts of his comrade Ramon Gris. Mistakenly believing Gris to be hiding with his cousins, he makes the untruthful statement to them that “Gris is hiding in the cemetery” (with the intention that they believe this statement to be true). As it happens, Gris is hiding in the cemetery, and the statement is true. Gris is arrested at the cemetery, and Ibbieta is released (Sartre 1937; cf. Siegler 1966: 130). According to L1, Ibbieta lied to his interrogators, although the untruthful statement he made to them was true, and he did not deceive them about the whereabouts of Gris (Isenberg 1973, 248; Mannison 1969, 138; Lindley, 1971; Kupfer 1982, 104; Faulkner 2013).

Taken from, and full explanation there, https://plato.stanford.edu/entries/lying-definition

Answer to your question title:

Well. Your intention was not of lying, but to ride the roller-coaster. So, you presented the fact (your height) in a way best known to you. So, you spoke an honest lie.

An honest lie or confabulation according to wiki article is,

https://en.wikipedia.org/wiki/Lie#Types

An honest lie or (confabulation) can be identified by verbal statements or actions that inaccurately describe history, background, and present situations. There is generally no intent to misinform and the individual is unaware that their information is false. Because of this, it is not technically a lie at all since by definition, there must be an intent to deceive for the statement to be considered a lie.

Confabulation means https://en.wikipedia.org/wiki/Confabulation

Confabulation is a memory error defined as the production of fabricated, distorted, or misinterpreted memories about oneself or the world, without the conscious intention to deceive.

Answer based on your explanation:

The example that you provided is of a trivial nature. Such lies are not culpable.

A fib is a lie that is easy to forgive due to its subject being a trivial matter; for example, a child may tell a fib by claiming that the family dog broke a household vase, when the child was actually the one who broke it.

NOTE to OP: Please update your example. So, it will be easy to select appropriate type of lie.