It may not be the majority of modern retail games that use Unreal engine (or some variant), but it could very well be a majority of the most popular games. Take the COD series, for example. Each year the latest COD game breaks sales records set by the COD before it, but if you look at the engine it uses it is based off a fork of Unreal engine.
A console's total software library will consist of hundreds of games, but in the end there's only maybe 100 or so of that which sell in significant amounts and anyone cares about. Maybe only 60-80 games use Unreal, but how many of those are within the top 100 games? There's a **** load of games like Elf Bowling and stuff like that which I'm sure don't use Unreal, but do these games matter? Nobody cares about shovelware games. They may make up the majority of games period, but they do not make up the majority of games which anyone gives a crap about.