Without knowing any more about your situation, you are probably experiencing one of two things:
1. Normal higher revs common to all hybrids in certain situations
2. Abnormally high revs caused by a problem with the software (very rare)
It's hard to say which situation you are in because "ridiculously high" is subjective, and each reader of your post will likely have a different picture painted in their mind what that means, which may or may not match what you are actually experiencing. Thus the comments and advice that you receive may vary depending on how each of us interprets what you are describing.
Possibility #1, those who have never driven a hybrid before are sometimes disconcerted when the engine seems to be revving higher for no apparent reason. In gasoline cars engine revs are directly tied to how far we press the accelerator pedal, whereas in a hybrid the engine sometimes needs to charge the battery, and on its own it may at times rev higher than might be expected. The Clarity is more susceptible to higher revs when the EV range has dropped to 0. And the engine can be especially loud when climbing a long hill or mountain with 0 EV miles. But you didn't mention climbing a hill when this happened, so I assume your high revs occurred in normal driving situations. Some people say they can avoid higher revs to some extent by always have some EV range remaining when they are driving in HV mode.
However I think most people in that situation would probably choose different wording to describe it, like "the engine seems to be revving higher than normal sometimes". Whereas you used the term "ridiculously high", which again is subjective as none of us know what you experienced, but if I am imagining correctly what you experienced it doesn't seem like it's the normal higher revs situation common to Clarity, especially if it occurred while driving on level ground at steady speed with more than 0 EV miles remaining.
Which leads to possibility #2. Some early owners of 2018 Clarity said that on occasion the engine would race very fast, they used terms like "redlining" and said that it was very alarming, to the point that they found a place to pull over and turn the car off and on again, which usually fixed it. Most other Clarity owners never experienced anything that extreme. There was no known fix or software patch from Honda, and yet for some reason we almost never hear about this problem anymore. One theory is that the problem was fixed by doing a "12V reset" which is done by disconnecting the negative terminal on the 12V battery for a minute or so. This seems to clear out data and has cured various odd software issues that people experience. It can perhaps be compared to rebooting a computer, although unlike a computer, just turning the car off and on does not fully reboot the system, thus the need to disconnect the 12V battery.
Which of the two situations you experienced I have no idea, I'm just letting you know what the two main possibilities are. If what you experienced seems more like the "redlining" situation, you may want to try a 12V reset. It doesn't hurt anything to disconnect the 12V, after all whenever the battery is replaced it obviously has to be disconnected. Just so you are aware the first time you start the car after reconnecting the battery you will receive all kinds of ominous warning messages making it seem like every system on your car is failing. Believe or not this is perfectly normal, and those messages should all clear within the first mile of driving.