Filtered out emails are being forwarded to my husband's account, even though I never see them because of the filter that deletes them before they reach my inbox

I have a number of filters created in Thunderbird, all of which filter email addresses for retail or political entities and deletes them. I never see these in my Inbox because of the filter. However, every once in a while, one of these emails gets forwarded to my husband's email account (maybe other accounts, but no one except my husband has told me about it)...except that I didn't forward the email. I never even saw it. When I check my Sent folder, it is there...forwarded to my husband's email address. How can an email be forwarded when the filter deleted it and I never even saw it?