Thank you for going to the trouble to find that. I wasn't sure how to search for predictions about how the Brexit vote itself would affect the economy, rather than the effects of actually leaving.

The article starts "Leaving the EU would hit British living standards" and only talks about recession (occurring in 2017) in the context of the "adverse scenario" they modelled.

As explained here:

https://www.independent.co.uk/news/business/news/imf-christi...

"[The adverse scenario] was predicated on the UK’s EU negotiations collapsing and the UK eventually crashing out of the bloc without a trade deal."

which hasn't happened (yet).

So I think the lessons to be learnt are that journalists can be guilty of over-simplifying economic analyses (presenting conditional scenarios as certain outcomes) and that government analyses can be self-serving (if they are published before a vote in which the government is campaigning for one side).