Or am I missing something?

You are missing something. Watch the programme.

The Bell Beaker folk come over as the ice receded over centuries, migrating slowly from the Ukraine area, when the Dogger Bank was Doggerland. The rising North Sea was held back by the ice until it could not hold back any more and the river volume cut the Channel. The influx of Celts** was a trickle, but those in what is now England, Scotland and Wales traded with Europe. And you know how fashion spreads. Technology especially. Human nature hasn't materially changed. We like bling, and farming gave us the spare time to accrue the wherewithal to trade, or build Stonehenge. And what Europe can do, we can do. Copy!

The languages we call Celtic are not necessarily related. Welsh and Gaelic aren't. As near as can be determined, the Scots are more likely to relate to Vikings. And they did invade!

Maybe the Programme chose their experts, but, experts they wus.

So has anyone tried to re-create the Bell Beaker language? Does any of it survive in English, Welsh, Gallic (sic) or Gaelic? Or Manx for that matter. I would wonder on such onomatopoeic words as pebble and babble but am no linguist.

** a term coined by historians.