Rhythm Typer is simply a rhythm game with typing game elements, overlapping the goals of each.
In a traditional rhythm game, the beatmap, when confined to a keyboard instead of a touchscreen, tends to be limited to either the arrow keys or some of the home row keys and spacebar. It normally makes sense to limit the number of keys so that the player can focus more on keeping rhythm rather than trying to find the right keys to press.
With a typing game, however, when given a known word, a skilled typist can quickly mindmap the right keys without much forethought. By using recognized words, Rhythm Typer makes the case that it can expand the range of possibilities in a keyboard-based rhythm game by utilizing the skills of a touch typer.
Luckily, there doesn't seem to be an overly-complicated overlap for error handling between the two genres of games. Both rhythm games and typing games focus on the accuracy of the keys typed or buttons pressed. Rhythm games merely use the timing aspect to handle the misses and are typically indifferent to other buttons pressed, so long as the right ones are pressed.
Typing games typically handle errors either with "full stop" (preventing progress until the correct key is typed) or "continue" (allowing the player to move beyond the mistyped letter). The game either will count all subsequent keystrokes as errors (forcing the player to delete mistakes to rectify them), or counting future correct keystrokes (allowing to the player to cut their losses with additional points after the typing error).
For a typing game to mesh with a rhythm game, with the all-important element of a timeline to pressure the player, the "continue" error handling with forgiveness of future correct keystrokes seems to be the logical choice, as either the other aforementioned error handlings would frustrate users after getting a single character wrong while the game forces them to keep playing. Stopping the music itself would also lead to choppy gameplay and would be too jarring for rhythm game players.