From what I heard there were two sets of information provided. Before the X1was developed US experts came to look at Miles proposals on the understanding that UK experts would later visit Bell. But the visit to Bell never happened. Then after the M52 was cancelled more information was sent to Bell.
The Bell X1 was designed with provision for a flying tail, just like the M52. But this wasn't enabled until testing demonstrated the necessity. Leading to speculation they copied it from Miles without understanding why it was used.