If you aren't familiar with the potential feud, Foley and Dean had a viral video of them having a confrontation in an airport, followed by a number of tweets back and forth between them. Ambrose's tweets contained threats to him and his family, saying he wanted to make his kids become homeless and orphans. The belief among dirt sheets at the time is that Foley wasn't okay with these comments and told Ambrose to stop, and he didn't and that's why Foley called off the feud.
Mick explained that he did actually have a problem with the tweets directed towards his family and he texted Dean asking him to stop. Ambrose continued after the text and had several tweets mentioning his family. Little to Mick's knowledge, Ambrose was working a UK tour and his cellphone couldn't receive texts. So Dean continued tweeting and working the feud on Twitter.
When Dean came back from the UK he pulled the tweets and apologized to Foley. The feud was still supposed to happen until Mick failed the impact test. The doctors told Foley he should never wrestle again. Foley would then go on to his own doctors who told him the exact same thing.
Foley said he was upset that he couldn't have the feud with Ambrose, but he believes it was best in the end because Ambrose ended up debuting with the Shield.