all tincymce’s switch when updating page after changing from html to text in custom metabox

This is, as you guessed, default behavior. It’s stored in the wp_usermeta table for each user in the wp_user-settings meta_key and does not differentiate between different editor instances.

On a side note, the tinymce version of wp_edior() does not cooperate very well with being inside a meta box. Especially if the metabox is moved, or hidden then shown, etc. I’d highly recommend either using the quicktags version only or not using a metabox (use any of a number of hooks in edit-form-advanced.php).