I think the issue here is that the same text string (js.discourse_reactions.reaction.too_many_request) is used both when a user triggers the rate limit by repeatedly adding and removing a reaction and when a user has selected the reaction that is used for ‘likes’ on the site and then reached the daily like limit. That limit is set by the max likes per day site setting.
I was able to trigger the issue that your user ran into by performing a similar action to what they did. It took a bit of effort to trigger the issue. I don’t think many users are going to run into it. That said, the error message that is displayed for this case is not accurate. The user has not exceeded their daily reactions (‘likes’) limit. All they have done is hit a Discourse rate limit that’s triggered when a user performs the same action too many times in succession. I think we need a separate error message to handle this case.