I.e., they have the same quality but different quantity, and German does distinguish vowels by length, so they are different sounds in the sense that two words that otherwise sound the same can be distinguished by vowel length. "Ratten" and "raten", for a relavent example, are not homophones and nor are "Massen" and "Maßen" (German learners might be frustrated to learn that in fact these two are opposites in some contexts).
A few remarks on methodology in linguistics (the science).
A phone is a class of sounds (as opposed to their instances which are all unique) that can be reliably described by articulatory or acoustic features (phonetics) or by patterns found in EEG (I'm thinking of MIT's voiceless mic).
A phoneme is another type of "sound" class used in linguistics and it is arguably the more important: phonemes, as studied in the context of a particular language, is the finite set of sounds (a few dozens at most) from which you build different words in that language. Phonemes always come in pairs, since they are defined as the minimal distinctive linguistic unit that can yield a difference in meaning.
Substitute /p/ with /f/ in/fear/ and you get /pear/, i.e. another word, a difference in meaning --> thus /p/ and /f/ are phonemes.
But substitute /r/ with /rrrrr/ in /Braveheart/ and you get the same word but with a scottish accent. These do not form a phonemic pair but allophonic variations of the same phoneme (here according to different geographic areas but they can also vary according to age, social status, gender, etc ...)
