Very bizarre - I've never, in fifty years of attending Speedway heard of anything like that before.
Perhaps the Referee should have excluded whoever tied the Advertisement on in the first place.
I can understand why he stopped the Race though - the only thing he could do for safety reasons - but - excluding the Rider seems ridiculous to me.
Perhaps someone with more knowledge of the Regulations may be able to explain this? Unless, of course, it come under the banner (see what I did there ) of, if a Race is stopped - then someone has to be excluded. If so, this is another example of some of the somewhat stupid rigidity of Speedways Rules.