Sorry, I was just going by the FA rules on the subject (albeit the 2013/14 version).
http://www.thefa.com/~/media/files/thefaportal/governance-docs/rules-of-the-association/2013-14/memorandum-of-disciplinary-procedures---section-a_b_c.ashx
But the assistant referee/linesman doesn't overturn anything; it is totally the referee's decision. Hypothetically, if the linesman were to have advised the referee that from his vantage point Stephens's play was, in his view, reckless/dangerous then it's totally up to Mike Dean whether and how...