I am confused whether you’re mistaken or just speaking unclearly. Boris Johnson has always belonged to the Conservative party. The Tories formed a coalition with the LibDems in 2010 because there was no majority winner in the Parliamentary election, but the LibDems were anti-Brexit. Even the Tories weren’t consistently pro-Brexit.
I'm guessing they're talking about Philip Lee [0] who was elected under Boris' government but defected to the Lib Dems when it became clear just how insane Boris was.
Liz Truss was Lib Dem early in her life but then went Tory later. Most of farage’s party are ex-Tories.
Peoples views change, and parties change. The Tory party of today is very different to that of thatcher, just like the republicans today are very different to Reagan’s
