japanese falls completely outside this generalization.
edit: on further investigation mama and baba are used very informally but it appears these are loanwords.
Also note: while 'mama' is a loanword it's overwhelmingly what babies call their mothers in Japan i.e. it has outcompeted other words likely for the same reasons as said in the article.
Personally, a phrase like "every language" immediately flags a BS sign to me.