What time was it? I think most trains ran yesterday didn't they? There seems to be have been a short gap early morning where a train terminated short and started at Finsbury Park, and that could have been just about anything. Maybe a driver arrived late because a taxi didn't turn up. Who knows?
I don't think GTR lies. Sure, they've milked a situation outside of their control by really emphasising it isn't their fault, but they don't lie outright. Train crew issues are stated as that. Operational incidents may be crew related but not a shortage (e.g. Driver stuck on a train outside the station to relieve the driver ahead) or train planning/rostering mistakes.
Are there actual examples of outright lies? How could they expect not to be found out?