Yes, you have a point that success in other fields would be good sign. But your example is a careless one.

You know, Einstein also invented a fridge

According to this io9 article, he did that in his late 40s to early 50s, after his great physics work was over. He was born in 1879 and worked on the fridge with Szilard from 1926 or after. It made the two physicists a bit of money but was not very practically useful. It certainly wasn't something you could have used to predict his physics success in advance, or that he did on the side while occupied with full-time physics.

Despite filing more than 45 patent applications in six different countries, none of Einstein and Szilard's alternative designs for refrigerators ever became a consumer product, although several were licensed, thereby providing a tidy bit of extra income for the scientists over the years. And the Einstein/Szilard pump proved useful for cooling breeder reactors. The prototypes were not energy efficient, and the Great Depression hit many potential manufacturers hard. But it was the introduction of a new non-toxic refrigerant, freon, in 1930 that spelled doom for the Einstein/Szilard refrigerator. The economics supported the freon-based mechanical compressor technology, and that's what most folks still use today.