gibberish

ジュニア小説の "A Wrinkle in Time" の一節です。
"But they're Mrs. Who's, they aren't mine," she explained, not realizing that her words would sound like gibberish to him.
"gibberish" が分かりませんので辞書を引きます。
Dictionary.com:
1. meaningless or unintelligible talk or writing.
2. talk or writing containing many obscure, pretentious, or technical words.
昔 "It's all Greek to me." と言う表現を覚えましたがそれを思い出しました。
Dictionary.comで "Greek" を引くと：
Informal. anything unintelligible, as speech, writing, etc.: This contract is Greek to me.
の説明があり、これは上の "gibberish" の１．と同じですね。