"keep what someone said" is available?

hi I'm in Japan and been studying English for some years.

In some forum in Japan

I respond "He doesn't keep what he said (the other day)"

when some questioner wanted to interprit a Japanese sentense.

But some answerer, probably Japanese and I guess not a English native,

responded that "keep what someone said" is never available.

He said it's an odd expression because "what someone said" has too wide range of its meaning

to specify and the verb "keep" as well so the sentence has such a vague meaning that listeniers couldn't get it even with some context.

I know "He doesn't keep his word/promise" is more appropriate

but isn't it any possibility that "keep what someone said" is available?

thanks