> The sorry was for interrupting and engaging you and having a favour to ask.

Sorry (heh), but it could easily be a sarcastic use (#4), not apologetic (#3) and not softening (#5). Not even tone can always differentiate between the apologetic "I'm sorry to bother you" and the non-apologetic "I'm sorry that your parents failed in raising you". They could be asking you for a favour, but they could just as easily be calling you inconsiderate of others because seats are for people not bags.