Yes, it really was unintentional. I guess that W had at some point used my phone to access her gmail account (linked to youtube) and it remained logged in. I only found out when at one time I googled something and got video search results, clicked on one, and was prompted to use YT app or browser. I clicked browser by mistake and later on noticed it wasn't my account. I never logged out and since then (many moons ago) it has of course remained logged in. Only post BD did I remember this and had a look at the view/search history.
BD - 30TH JAN 2015 S - 30TH JAN 2015 PA CONFIRMED - 16TH FEB 2015 (SINCE AT LEAST OCT 2014) CONTINUAL TALK OF D ME: 31 W: 28 T: 10yrs M: 4.5yrs D:5, S:6