I'm sorry, I have no idea and this isn't at all helpful, but I just have to say that I hate it when people refer to it is as "sausage toad"! At least the name "toad in the hole" conjures up an interesting image in ones mind, not like "sausage toad" that conjures up no image whatsoever.
toad in the hole? - because it looks like a toad in a hole, right? as much imagination needed as is for 'devils on horseback' [prunes wrapped in bacon] anyway :-)