Hmm? I don't think anyone considers ㅈ as three strokes, unless they're writing ㅈ like printed font. When handwritten, the whole フ-like shape is one stroke, and the small attachment is the second stroke.

Traditionally, one stroke means one movement between the brush touching the paper and lifting off - for example the Chinese character 弓 has three strokes: https://en.wiktionary.org/wiki/%E5%BC%93#/media/File:%E5%BC%...