Do add to carts and orders only count the product I'm testing? (Essential CRO Split AB Testing app)

No. Results are counted per visitor, not per product.

Once a visitor opens a page in your test, they're assigned to A or B. After that, any product they add to the cart and any order they place is counted for their version, even if it's a different product.

For example: a visitor opens the tested product page and is assigned to B. They then buy another product. That order counts as a conversion for B.

The Add to cart rate and Conversion rate show the share of visitors in each version who added to cart or ordered at least once.