Yeah, because it's a Liquid wallet, not a lightning wallet.
It's not actually "them" charging though, it's Boltz who's charging the fee.
Discussion
Ahh
Yep, you can receive Lightning transactions, but those are insta-swapped to Liquid by the Boltz service (involving a fee)
and you can send Lightning, but those are then swapped from your Liquid-balance by the Botlz service (involving a fee).
It works and does so incredibly well, but it'll cost you some sats.