Hypothetically speaking

Solution 1:

Language is a means of communication, but the same set of words can communicate different things - even contradictory things - at different levels.

hypothetically adverb By imagining a possibility rather than reality; as a hypothesis. - Lexico

At the immediate level, the preface of "hypothetically speaking" marks the communication as merely theoretical, not real.

However, just because someone calls something hypothetical doesn't make it so. Depending on the context, it could even mark something as not really hypothetical. So at the broader level, the "hypothetically speaking" preface can trigger the suspicion that it isn't.

Your question is whether labeling a matter as hypothetical in English is lying if the matter happened to be non-hypothetical.

At the level of pure linguistics, that's making a category error. Hypotheses posit something. Whether the hypothesis is true isn't relevant - the posited condition is merely considered academically.

If we go beyond pure linguistics, we could say that the way the language is used suggests evasiveness. Certainly, phrases like "hypothetically speaking" and "asking for a friend" have suffered 'euphemistic degeneration', where the euphemism no longer shields the hearer (and hence no longer shields the speaker) from whatever the more explicit version conveyed. However, going much further than this would bring us beyond the remit of EL&U, so that should be a discussion for a different forum.