question first to get your mind prepared for the answer:
if you have $100 in your pocket. does it have to be categorically only in the format of a single $100 bank note. or can it be a measure of a allotment of smaller amounts?
if you had a tonne of gold does it have to be a single brick weighing a complete tonne. or a measure of smaller amounts like kg, ounces, grams that total a tonne?
answer:
in code/value in binary of actual data relayed/stored, whether its stored in the UTXO, mempool, blockchain databases or relayed.. wait for it..
there are no hard data "btc" it is all relayed and stored in units called sats..it is the software GUI(display) code that then converts it to convenient formatted number for easy reading.
what tadamichi left out of the quoted code in his post. is the part where COIN is just an expression of hard data in blockchains, utxo's, mempools converting into COIN by doing a /100,000,000 of the hard data
https://github.com/bitcoin/bitcoin/blob/master/src/consensus/amount.h#L14/** The amount of satoshis in one BTC. */
static constexpr CAmount COIN = 100000000;
(i hope tadamichi sees my example of how i, someone that is in full adoption of bitcoin can atleast be open and honest about how bitcoin actually works without having to pander to uptopian stuff, and maybe he takes this as a lesson that trying to slide things under the rug can be misleading for his favoured network)anyways
none of the unconfiirmed transactions relayed around or put into mempool databases.. nor the blockdata containing confirmed transactions nor the utxo data for easy indexing of the unspents remaining are in btc denominations.
but then again. do people care about a tonne of gold if its not in a format of actually being one single lump of hard gold or do they still call it a tonne of gold if they have 1000 bricks of 1kg of gold or 35274 ounces of gold
we are actually approaching an epoch(point in time) where people are not even able to afford to "buy a whole bitcoin" where people naturally are going to use different terms like sats(single units) and bits(100 units).
much like no one really cares about the "Tonne" when they are buying ounces of gold
btc is not and does not have to be a physical single lump. just like a gold "tonne" does not. its just a measure for easy conversation and display and easy accounting for human eyes and brains to understand using less long numbers.
..
now with that said..
blockchain, utxo, mempool databases and relay data streams all show actual units. (yes measured in sats) but they are actual units. that can be seen. and so if someone has grouped together an allotment of 100,000,000sats then they do indeed own a bitcoin
if you gather together 35274 ounces of gold, then you do indeed own a tonne of gold.
if you have in your left pocket 7 bank notes different denominations of 1x $20 and 6x $5. and in your right pocket you have 500 dimes in your right pocket.. you do indeed have $100 in your pants.... it does not have to be a single $100 bank note to be called $100 in your pocket