Have a good one

Sometimes I’m perplexed when after thanking someone for helping me, instead of “You're welcome”, out comes “Have a good one”. Does “one” equal “nice day” ? If so , maybe his view of a nice day is not the same as mine, in which case the probability exists that he is wishing me a lousy day. I doubt that, but there is a high probability that he really doesn't give a damn about my prospects for a nice day and merely would like to see me go on way. It goes without saying (but I‘m going to say it anyway), that at best “Have a good one” is nebulous and presumptive. I submit that “You're welcome”, is brief, to the point and leaves no doubt about the intent. Having said that, have a good one!