If they weren't invited in, the British invaded a part of Ecuador. Invading another country's territory is generally regarded as the senior act of war.
For their own protection, Ecuador should round up and detain all British subjects on their sovereign soil as potential spies and saboteurs until the illegal seizure of one who they had granted asylum is remedied.
"...After 2,487 days in the embassy, the 47-year-old was arrested after Ecuador revoked his political asylum and invited Metropolitan police officers inside their Knightsbridge premises, where he has stayed since 2012 to avoid extradition to Sweden over sexual assault allegations which Assange has always denied..."
I was kind of wondering the same thing, but no, the Ecuadorians kicked him out. Sounds like he refused to leave, so they invited the British authorities in.