It isn't "spiritually" true. It is
factually true to the extent that the High Court ruled 350m was approximately the correct gross figure. Indeed some say that figure is conservative because it was based on projections from an official figure dated from 2014 that put the gross at closer to 450m. I'm guessing 2014 was high because of financial bailouts still being paid into the EU coffers.
From the ruling statement:
“The alleged offence set out in the Application for Summons is that the Claimant “repeatedly made and endorsed false and misleading statements concerning the cost of the United Kingdom’s membership of the European Union”. It appears that if the Claimant had said/endorsed a figure of £350m per week gross, or £250m per week net, there would have been no complaint.”
https://www.judiciary.uk/wp-content/uploads/2019/07/2019ewhc... (search in doc for "350" to find the juicy bits)