There may be a transference of sleep data between partners, especially if one partner tends to roll over to the other side of the bed. Your partner sitting in the middle of the bed could also register data for both sides. Since our data is based on presence in the bed, it is difficult to eliminate the transference of data completely.
You can also update your sleep data by scrolling to the bottom of "Last Night" and selecting "Edit session." This will correct it for yourself and also provide us with valuable feedback to help improve the algorithms going forward!