looks to me like Ralf & Florian (is it?) have got bass traps in the bottom right-hand corner of that room, under and to the right of the speaker. And possibly something under the speaker in the left hand corner. Looks like it probably has a decent-height ceiling too.

The person I know of that gets the most impressively "professional" sounding acoustic recordings is Ben Walker, who plays with Josienne Clarke. His "studio" is his bedroom, he has OK mics, but nothing extravagant. Yet it sounds terrific.