Allow me to quote this article.
And it says.
Eli Nagar, CEO of Braiins Mini Miner, revealed that he and his team gave Schiff one of their portable rigs. It’s unclear if it was a gesture of goodwill, next-level trolling, or simply publicity.
Some doubt if Schiff will ever use the product, and others joked he may sell it for gold. Nevertheless, the gift now officially makes the Bitcoin critic an official owner of a BTC mining device.
More info is here
https://blockzeit.com/peter-schiff-admits-to-owning-bitcoin-and-gets-a-btc-miner/So I think its not verified that Schiff is mining Bitcoin and maybe they made that post as part of their publicity stunt since they provably could get lots of attention especially if they can convince Schiff to operate a Bitcoin miner at home.
But I still don't believe on Schiff claims since he provably just want some exposure from Bitcoin community.