It was the case just a year ago when I flew out of LHR. US flights were out of terminal 5 and a special pre clearance zone. I’ve been through Frankfurt’s pre clearance as well. Maybe things have changed very recently? It flew under the radar if that’s the case.
Maybe? I've flown out of Europe to the US many many times and never encountered any special security measures. Certainly not LHR (Terminal 2 usually I think) and not Frankfurt just a few months ago.
