That sentence is fine. There may be more technical analuysis, but I'd say the "too" is being used as a tag, and it means "as well" or "in addition" - so in this case it could mean 1) I saw him more than once this week, (on a day other than Friday) 2) I saw him at a disco as well as at the pool. 3) ( less likely) I saw HIM as well as some other character you spotted at a disoc on a Friday!
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.