I would not be able to cite any actual factual evidence, because there is no evidence that any Japanese-Americans actually did spy for Japan. However, I think you can make a very compelling argument that early 1942 was no time to be taking chances.
At that point in the war, the US was losing badly. They had been surprised by the attack on Pearl Harbor. Because of these two things, they would have been worried and they would have been unsure as to what might happen next.
From our vantage point nowadays, we can see that the Japanese-Americans had not done anything and that Japan had not intention of invading the US. But how were the Americans to know that at the time?