The marriage is wrongly cited by FamilySearch.
It wasn’t in Essex, and it wasn’t non-conformist. It was in the Anglican Church of St James, Westminster, Middlesex, on 30 September 1710, with an Archbishop of Canterbury’s licence:
John Nelthorpe of St Margar(e)t W(estminste)r
Ann Heather of this P(arish) p(er) L: A: B: C.
The image of the marriage register is on Ancestry. The licence index (on FindMyPast) shows that the licence was issued through the Faculty Office on 28 September 1710.
The allegation for the marriage licence may show whether John Nelthorpe was a bachelor, but there’s no online access. You can order a copy of the marriage allegation for £15.00, or view it at an LDS Family History Centre for free.