Timestamp between android and iphone

Hello everyone. My bf has an android phone and i have an iphone. We use to send messages through f/b regural apps not messengers but not on online chat only through messages. At the timestamp of his phone when he has an internet connection i see him active 2 min or 3 min before or active now etc. He says sometimes he is not on F/B but of course he receives push notifications in his phone. Many many times i see him active for example 1 min ago or active now but he says he is not in the app. Is there anyway that F/B app "thinks" that he is active when he received notifications but not entering the app itself??? Please if you can help me i would be grateful.