Spotlight conversion in UK units
1 pint varies by country and Spotlight clearly does not use language settings to determine the correct value for 1 pint. It is 473 ml in USA and a few other countries.  See Wikipedia.  In Australia it is 570 ml, in the UK 568 ml, in India 330 ml and the list goes on.
I have submitted a Feedback Report to Apple FB9020879 and will report in comments what response (if any) that I get.
US measurements derive from usage in Britain before the War of Independence. The units were defined in 1707.  Britain changed some definitions in 1824 to the current Imperial units whilst the USA kept to the earlier system.  A bit like spelling changes where Britain has changed since 1776 but the USA has remained more consistent with older usage.
Just to make it harder for Apple, here in Australia, a pint glass of beer is 570 ml, except in South Australia where it is 425 ml.
I trust you don't consider this history too irrelevant in a technical forum, but @CaptainProg has referred to his interest in brewing.