That seems believable - the UK saw 390 million passenger rail journeys in the last quarter [0]. Amtrak saw just under 23 million in all of FY22 [1]. That’s before accounting for the UK having a population around 1/5 that of the US.

[0] - https://dataportal.orr.gov.uk/statistics/usage/passenger-rai...

[1] - https://www.amtrak.com/content/dam/projects/dotcom/english/p...