I don't remember Farage or anyone else saying exactly that but there was a concern that refugees granted EU passports in other EU countries might then use those passports to later access the UK while it was still part of the EU.
Since 2015, after Merkel opened doors to Germany, and so, through Schengen, to the EU, the people smugglers have organized much larger numbers of paying migrants from all over Asia and Africa into the refugee mix, and into the EU. Many of these people seem to be set on making it to the UK; the people waiting in the sand dunes near Dunkirk reached there easily because of Schengen, which enables unchecked travel across continental Europe. This freedom of movement within the EU makes like too easy for the smugglers and appears to not help genuine refugees so much.