The sentence focuses on a specific span of time, namely the time that runs up to the speaker’s arrival in Japan, and also contrasts it, by は, with the time that follows. In addition, the second sentence specifically states the speaker did see the sea after they came to Japan. Then, it would be much more natural to describe their earlier lack of experience as a past state using the past tense ありませんでした.
In the examples in the linked question, the speaker did experience something during a time vaguely referred to as “earlier” (以前) or more specifically before some event happened in the past (e.g. 仕事で大阪に引っ越す前). Either way, this necessarily means they do have the experience in the current state, too. This reduces the difference between the two tenses to that of emphasis as the accepted answer suggests.
The two tenses are not so interchangeable in your example because of the contrast between the past and current states.