Japanese is always read from right to left (unlike Western languages, which go from left to right). So the same system applies to manga comic strips.
You might even have read one the wrong way round! When Manga comics are published outside Japan, the pages and strips are inverted, to make them ‘suitable’ for Western readers. This distorts page layouts, originally designed the other way around. But, as Manga has become increasingly popular, more publishers have decided to keep the original direction and respect the author’s designs.