I thought "small values of energy" <=> "long wavelengths"? And for a body of a low temperature T, the maximum is for long wavelengths, so it can't be that either.

Whilst for small values of the energy and for short waves, Wien's law was satisfactorily confirmed, noteworthy deviations for larger wavelengths were found, ...

Note the use of "and" rather than "i.e.".

Wien's law describes the spectrum of black body radiation. While it is accurate at short wave lengths (high frequencies), it is not accurate at low frequencies. Wien's law is a good approximation for black bodies that are radiating a relatively small amount of total energy. When the total energy output gets larger, the failure of Wien's law to predict contributions by low frequency waves becomes apparent.