I would contact your case officer asap and explain that he does have a conviction.... (dont know what you will say as it clearly says including any conviction removed from records and with it only 4 years ago it isnt like you have forgot about it).... that said i don't think it would stop you getting a visa.... People get visas with much worse records than that but it is usually longer ago and declared on the visa application.... Maybe as mentioned earlier speak to a goog migration agent (Go Matilda) and get help so you don't make any more mistakes or forget something else.... Good luck I hope it works out for you.