We must remember that Andy wasn't in a good place or state of mind when he decided to voluntarily check-in to the mental health unit on September 25th. There were signs that he has wanted Robert dead for quite some time. It seems unlikely to me that Andy would fully recover from his mental health problems after having been in the mental health unit for just several days. Right now, we don't know what Andy was going to tell Pete when they were sitting by the lakeside this past week on 8th October. If Andy was ready to tell Pete something like involvement with Robert's shooting then just imagine what could come out from Andy after a few pints in the Woolpack to any nearby witnesses under the right circumstances? When people say "I did that because I was drunk", what they really mean is that they did that when they were drunk, and it only came out because they were uninhibited then but it was inside them waiting to come out eventually. Similarly, if Andy sometime gets hypnotherapy or similar treatment who knows what could come out from him then? Andy has previous bad history and problems anyway. He killed his step-mother in a barn fire (in about 2000) and was also a passenger in a car joy-riding incident in which his school headteacher (also female) was killed. Andy also beat up girlfriend Jo Stiles. He also had a breakdown and lost his farm, eventually becoming a labourer for Butler's Farm and working for the Bartons. Andy has many issues, maybe not least of which is that he is not a Sugden by birth or bloodline but is a fostered child, real name Andy Hopworth. Is it any wonder then that he and Robert Sugden have issues even to the present day, when all he seems to see is that Robert has managed to outdo Andy and to do well for himself and to seemingly take everything from Andy that Andy has ever managed to get for himself in life? Andy and Robert are two opposites really. Andy is the local lad happy to settle with a wife and kids whereas Robert forever wants more and bigger and better things. As such, a clash between their personalities seems inevitable, even if means a head-to-head battle to the death.
If Andy did set something up by phone from the mental health unit on Thursday September 25th to someone's mobile phone then there would maybe be a record of this in the phone network to surface in due course. History shows that there are not many (or any?) secrets in Emmerdale which last forever, and every secret there seems to come out eventually.
Source:
Andy Sugden
https://en.wikipedia.org/wiki/Andy_Sugden