Yes. It is a master public/private key pair which it is displaying.
So if I want to back these up manually using the clipboard, then these are the only keys I need to back up for the HD account in question, correct?
It is currently saying '"Contains 3 private keys"
Is there any reason to locate and backup those 3 individually generated key-pairs? Are they forever hidden in the app?
If there's another Bitcoin fork then you might need those individual keys, it depends on how the wallets choose to incorporate it.
In almost all cases all you'll need is the seed.
If you really need individual keys then this will extract them -
https://github.com/iancoleman/bip39 but it doesn't discriminate between used keys and unused ones so you may be in for a lengthy search.
If I understand what's going on here, you're planning in the event of a fork to locate the keys for all the addresses in your wallet that have funds in them.
I would start by getting a list of addresses with funds, which you can use to to sort out the keys that are useful.
Go to the Accounts tab, click on the HD wallet, click the menu icon on the upper right, and click Show Unspent Outputs (aka UTXO). This will give you a list of all the addresses in your HD wallet that have funds in them. If you then have a long list of keys to sort through to figure out which ones have funds and which ones don't, the logical thing to do is generate the addresses from all those keys, and then sort that address list against your UTXO address list, just keeping the keys to the addresses that are on both lists. If the UTXO list includes addresses that aren't in the mnemonic converter list, then something went wrong, like you used the wrong derivation path or something. Mycelium's UTXO list is the primary reference.