GRAMMAR DETAIL

～かと思う

thought that; assumed that

Follows interrogative content to express an assumption or judgment held before the facts were confirmed.

Examples

鍵をなくしたかと思ったが、ポケットに入っていた。

I thought I had lost my key, but it was in my pocket.

会議は中止になったかと思いましたが、予定どおり始まりました。

I thought the meeting had been canceled, but it began as scheduled.

誰かが来たかと思ったら、風の音だった。

I thought someone had come, but it was the sound of the wind.

Structure: A tentative proposition takes か, quotation-marking と, and 思う.
Basic usage: 鍵をなくしたかと思ったが、ポケットに入っていた。 describes suspecting the key was lost before finding that it was in a pocket.

The assumption and its correction
- なくしたかと思った states the earlier thought, while ポケットに入っていた supplies the actual situation. Read the conclusion that the thought was mistaken together with what follows.
Distinct from asking directly
- 来たかと思った reports wondering whether someone had come. It differs from a direct question requesting an answer, such as 来ましたか.