Meaning of "He's got more bottle than a milkman"

It could be that it comes from when beer made by Courage came in bottles. http://aldertons.com/home/slang/

If you want milk, put the Ari on the doorstep. [Every now and again they throw a curve at you. One person has suggested that, not being familiar with Aristotle, early Cockney's might have assumed the name was Harry Stottle! Heard from John Mahony who says that when one uses the expression "lose your bottle" it means to lose the contents of your arse, i.e. "he's shit it", but Ken Caleno says it means to lose your courage (from Courage's bottled beer)]

It is Cockney rhyming slang, from "bottle and glass", which rhymes with "arse". So it is an inoffensive way of saying "arse", which in this context means "courage" (I'm not quite sure why).

It is common in the phrase "to lose one's bottle": "I lost my bottle completely when I saw the knife in 'is 'and." Any native speaker of British English would understand it (although I don't think they would all know its origin as rhyming slang).

Edited to add: After reading the answers at this link from @StoneyB's comment, I am less certain about this than I was.

It may be that the Commentator meant that this particular player has even better shots compared to his opponent who may be more experienced & matured . Even I believe you must elaborate the two players about their age/stats and the scenario. The Phrase clearly shows that the Milkman is always the man who carries more bottles of milk and delivers door to door . No other person has more milk compared to him . When compared to Milkman it shows that this Player has more bottles means he has more calibre , more capacity and potential compared to his opponent or his existing contemporaries .