Yes putting 30k on a horse would be a big gamble... and fairly irrelevant to what is being discussed.
It was your statement that there was no risk which needed correcting.... lottery tickets are also a bit of fun, they also have a risk associated with them - your friend could also choose to gamble weekly on lottery tickets to the equivalent amount he's risking in terms of interest payments he's forgoing by investing in premium bonds... He may or may not have better chances that way - I'm not interested in checking at the moment but a previous poster is asserting that the lottery provides better value and on the face of it he seems to be right.
Better still might be sports betting... the bookie's over-round is minimal compared with the amount of money siphoned off in the lottery... probably a bit more fun than either premium bonds or the lottery too though you don't have the extreme outlier prizes.