The Lore Bard goes first and casts a high-level spell, which the sorcerer attempts to Subtle counterspell with a lower level spell slot.
Since counterspell only has a somatic component and the Subtle Spell metamagic option removes that, the counterspell is not detectable by the Lore bard. The sorcerer also has to roll an ability check (as part of counterspell) in order to successfully counter the bard’s spell.
However, could the Lore bard still use his Cutting Words feature to remove a Bardic Inspiration die on the sorcerer’s counterspell ability check, even though the Bard does not know that a spell is being cast?
The same question also applies to other spells with only verbal/somatic components (which can be Subtle Spelled) that include an attack roll or ability check to function, such as dispel magic or chaos bolt.