1. Communication is key here - it sounds like you have a breakdown in communication with your manager, or a breakdown in their understanding of your work.
2. You're attempting to turn something very specific (please fix this bug), into something very abstract (some bugs can't be fixed, some bugs take longer than expected to fix). That's not going to help, particularly if this was in the end a simple fix, it just makes you look obtuse and out of touch.
3. The manager's proclamation is probably born of frustration with previous experiences where bugs were not fixed quickly and they have no idea why. Communication is the answer - if you communicate before and during a bug fix, they won't wonder why, they'll know why if it is not fixed, and they'll know what you are working on or have to sacrifice to make that happen. They'll know when you are installing logging to track it down, or when you eliminate modules one by one in tracing it, they can follow along and explain to their manager why it is not yet fixed.
4. You need a process which you both agree on for escalating bugs or setting priority - this clearly isn't it, but what is it?
Instead of complaining to them if you possibly can fix this bug quickly (perhaps you already did), then talk to your manager privately about process, talk to them about timeframes and how best to frame them, and try to find a process that works for both of you. That process will involve compromise on both sides - the manager accepting that sometimes things go wrong, sometimes bugs are difficult to pinpoint, and that scope/quality will sometimes be cut to deliver on time, you accepting that your job is to communicate upwards (particularly when things are unexplained), and accepting that sometimes corners will be cut on quality to deliver on time, and some things which are important to devs are not as important to the company, and that schedules and estimates are required, even if they can never be completely accurate.