Could be, but @mxchive is used for both deposits and withdrawals. Besides, I can't find any transactions between @mxchive and another possible MXC wallet. I also searched for other accounts with 'mxc' in the accountname, but could not found any other wallet.
Finally, I looked at a list of the largest transfers per day I don't see any large HIVE transfers to a possible other MXC wallet.
I think this is their only wallet.
Could it be that they had STEEM and got the airdrop?
@mxchive was created on april 16. After the hard fork, so there was no airdrop on this account.