This is a recurring thing, not a one off.
Generally speaking, WK tend to break down kanji into their radicals, even when there’s the possibility of instead using other kanji as basis for their mnemonics.
Alternative ways of learning kanji might be advised where the item is not broken down into its radical parts, but which rely on knowing other kanji. For example, using the Keisei-script helps with recognition of the kanji composition. It won’t give you mnemonics, but it will allow you to easily recognize cases like this and bring up even more similar cases/similarities between kanji, the relationships of their readings, and from there you can get a head-start on learning future kanji as well as make your own mnemonic.