X350 windscreen replacement - hot/cold/running water?

My 2003 X350 screen cracked last week. Autoglass take vehicle details and book me in. Ask me if it’s heated, I say no. No switch on console, no elements visible. It does have a rain sensor, though. Install booked to happen at the garage that was servicing it, as a lot easier than doing it in a London street…
They turn up with new screen, but find 2 x connectors pre-install and say it’s the wrong one as mine is obviously heated, and leave. They’ll get the right one and return in 48 hrs, I’m baffled, but apparently my screen has wiper park heating. Never knew that.
They return as promised, then call saying it’s wrong again and leave. Eventually transpires that Jag no longer supply my old screen, only fully heated or unheated screens. So, fitter returns with second screen (heated) and we agree to fit it. They say that he’ll connect the old tags to stop them hanging around loose, but it won’t work. No big deal as I never had screen heating anyway.

When I collect the car, garage owner asks why they’ve connected up a heated screen to the wiper heating?

They have a worry that if I turn on the rear screen, it may also turn on the full front screen heating, drawing a lot more current than the wiper heating did, causing future problems.
Autoglass say it shouldn’t, they’ve done it before and it simply heats up both screens but slower than usual. If a fuse does blow, they’ll disconnect the new screen.

Who is right? Is connecting a heated screen to the wiper heating OK?
My feeling is that if it does not have a separate switch it isn’t. But I don’t fit windscreens.

Paul