He used the past tense because it is indirect speech. Indirect speech is when we don't quote someone's exact words but paraphrase what they said. So that we know it's indirect speech in conversation, because conversation doesn't have quotation marks that we can see, it is normal to backshift the tense.
Direct Speech: You said, "John speaks English."
Indirect Speech: You said John spoke English.
In the above example, it's unlikely that John has forgotten how to speak English. The reason for saying "spoke" instead of "speak" in the second sentence is so the listener can more readily determine that the speech being reported is indirect speech, not exact words.
I've included a link that explains "indirect speech" and the rules that apply. If you read it, you will more readily understand. Scroll down to the heading "Examples" and then pay particular attention where it talks about "backshifting."
The Education First website also provides an explanation of indirect speech and backshifting the tense when reporting indirect speech.