In the C1 writing challenge "A Ghost Story" the partial sentence "While I was pulling weeds" in the context "While I was pulling weeds ... I heard..." was translated "Tandis que j'arrachais les mauvaises herbes". "Alors que" was also suggested but my answer "Pendant que" was not. Why is that?

Larousse (https://www.larousse.fr/dictionnaires/anglais-francais/while/624050) translates "while" as "pendant que" when it refers to a simultaneity of time (e.g. pendant que vous serez à Londres il faut visiter le British Museum), whereas "tandis que" and "alors que" it says are applicable to the case where "while" is used in the sense of "whereas" (e.g. elle est de gauche tandis qu'il est conservateur).