The IMF hates bitcoin because it takes power from them so it wouldn't surprise me at all if they are lying about it. Their credibility - both with regard to bitcoin and economics in general - is zero.
Yes, it is no secret or surprise that the IMF has always hated and opposed bitcoin but I don't think they are lying. If you notice, it has been days since the IMF made this announcement, but El Salvador has remained silent and has not given any response. What does this prove? In my opinion, Nayib Bukele's silence means that they have admitted that what the IMF said is true, and keeping quiet and letting things go is probably the best solution for them at this time.
Previously, Nayib Bukele stated that they still buy bitcoins despite warnings from the IMF and judging by his character, if the IMF is lying, he will not stay silent like that.