Did Japanese have some other word that meant "kitchen" that the English word somehow displaced? Did Japanese people not have any use for a word that referred to a kitchen prior to contact with English speakers? What's going on here?
This question makes an assumption that "kitchen" (キッチン) is the standard Japanese word for kitchen. This is mistaken.
The Japanese word for kitchen is "daidokoro" (台所ーroughly, "place of stacked plates". This is a word that has its origin in the Heian era and is in common usage today. The word "kitchen" (キッチン) is also in common parlance but is used interchangeably with daidokoro.
The use of Western loanwords in parallel with original Japanese is a characteristic of the language (this older answer provides some additional context). Someone may use the word "kitchen" over daidokoro in some contexts to convey the nuance of Western style or to market it as being more modern, but they are effectively interchangeable.