That is true, but struct{} is the unit type — not the bottom element of the interface-type lattice.
struct{} can be added as a field of any struct with no effect on comparability or equality, and adds no bits of information (it is a multiplicative unit).
As an interface value, struct{} carries one “bit” of information: its type.
But struct{} has no methods and is not assignable to any interface type: therefore, it is not the bottom type of the interface lattice.
In contrast, the interface of the empty type-list, if such a thing could exist at run-time, would presumably have only one value as well: the nil interface value.
The nil interface value is a member of every other interface type, so the empty type-list would be assignable to every other interface type (it is the bottom of the interface lattice).
Conceptually, it has all possible methods, but there would be no point in calling them: they all result in a nil-panic.
As a struct field, the empty interface is also a multiplicative unit (it adds no bits of information).
However, it is also an additive unit: the union of the empty type-list and any other interface is identical to the other interface (because every other interface already admits the nil interface value).