The Supreme Court was fully aware of the technical term:

Botanically speaking, tomatoes are the fruit of a vine, just as are cucumbers, squashes, beans, and peas. But in the common language of the people, whether sellers or consumers of provisions, all these are vegetables which are grown in kitchen gardens, and which, whether eaten cooked or raw, are, like potatoes, carrots, parsnips, turnips, beets, cauliflower, cabbage, celery, and lettuce, usually served at dinner in, with, or after the soup, fish, or meats which constitute the principal part of the repast, and not, like fruits generally, as dessert.

The attempt to class tomatoes as fruit is not unlike a recent attempt to class beans as seeds, of which Mr. Justice Bradley, speaking for this Court, said:

"We do not see why they should be classified as seeds any more than walnuts should be so classified. Both are seeds, in the language of botany or natural history, but not in commerce nor in common parlance. On the other hand, in speaking generally of provisions, beans may well be included under the term 'vegetables.' As an article of food on our tables, whether baked or boiled, or forming the basis of soup, they are used as a vegetable, as well when ripe as when green. This is the principal use to which they are put. Beyond the common knowledge which we have on this subject, very little evidence is necessary or can be produced."

Nix v. Hedden, 149 U.S. 304 (1893)

So this is how the Supreme Court could do this: they were fully aware but reasonably decided tariff laws should be based on ordinary meaning.