Haha, it made me laugh. It's sad that he died though, he was a great man IMO.
Yeah, Bob Crow was a trade union leader who used to threaten to cause strikes fairly often. You'd get all these train strikes (like one that happened fairly recently) that'd drive London to a standstill.
Everyone would have to walk or get on replacement bus services
I read the joke as meaning that the guys carrying his coffin have to take the bus because there's a train strike going on xD
My mum loved him because a few years back the strikes got her the occasional day off work ^^