The email TfL sent [1] to traintimes.org.uk ISP looks like a catch-all sent in haste. For example, it doesn't even mention the map. Instead, it invokes trademark registration numbers but these resolve [2] to LONDON UNDERGROUND and UNDERGROUND wordmarks and the roundel, none of them covering the map geometry as far as I can tell. It alleges a violation under Anti-Cybersquatting Consumer Protection Act [3] but the act only applies to domains - and TfL never claims "traintimes" to be an infringing domain name (certainly doesn't look so under the marks cited). And, as a sibling comment points out, the act is a U.S. law but the site appears to be hosted in the U.K.

If you think you have a case about the map, why not state it explicitly? The cynical answer is that ISPs have incentives not to care so making a case doesn't matter but ...

[1] https://traintimes.org.uk/map/tube/email2.txt [2] One can look them up in https://www.tmdn.org/tmview [3] https://www.law.cornell.edu/uscode/text/15/1125