Being at work would imply that you have a reasonable expectation of privacy, unless that work is in a highly public setting or the training was being conducted in a public setting (such as a public auditorium that was rented for the event) instead of a private setting (such as in a conference room not accessible by the public).

Not 100% related to the initial post, but is related to this portion... my job announces that they are recording a webinar/lecture/training etc because it will be posted later for others to watch or listen to. Thus, not only do you consent for those present to hear and see you interact with this material, you are consenting for all future parties who will later watch the recording... hope that makes sense.

Web meetings will also often take into account that participants may be from other states, usually the policy is designed with the most restrictive state laws in mind which may not be PA.