Hi Zoe!
Could you please head over to https://h5p.org/forum if you want to ask for support that’s not specifically addressing the H5P plugin for WordPress? The H5P content types running inside this plugin environment are not bound to WordPress but also work on Drupal, moodle, Typo3 with the respective plugins, so you will have much higher chances of getting answers there.
For this one: You need to a) for each draggable select where it can be dragged to and b) for each dropzone select which draggable would be correct there. I assume you just selected one dropzone for the draggable that you are referring to, so it feels as if the correct solution was highlighted.
Feel free consult the documentation for more options. You could, for example, deactivate the highlighting alltogether in the behavioral settings.
Best,
Oliver