Like, they could've just said 蕎麦屋 rather than そば屋 if that restaurant is selling dishes involving soba noodles for example. I've seen うなぎ more often when there's a Kanji for it (鰻) but decide to transcribe it using Kana, same with supermarkets or stores on them writing たまねぎ (玉葱), にんじん (人参), りんご (林檎), まぐろ (鮪). Also stalls that sell takoyaki often write it as たこ焼き (they've could used the Kanji for たこ which is 蛸).