For the two different interpretations of this proverb see upsilon 28, upsilon 29. This lemma (with upsilon 29) gives the more probable. Its first full sentence is taken from Photius, Lexicon kappa1114 Theodoridis, but omits the initial dei= necessary (as Porson realised) to make sense. Both sources ignore the distinction made by Herodian (On the declension of nouns 3.2.733.4-5,29-30 = Lentz's edition 1.36) between *kro/twn, the S Italian city (and its eponymous hero) and krotw=n, the 'little beast' or tick, referred to here, probably a species of Ixodes or deer tick (but see kappa 2483). This distinction is observed in Menander's Lokrians (fr. 263 Koerte, now 223 Kassel-Austin), where the proverb refers to a tick; cf. Koneiazomenai 6.
Photius in a later entry (cf. upsilon 28) compares this proverbial expression to two others: "sounder than an unripe grape (o)/mfac), or than a (round) gourd (koloku/nth)." He thus takes them to refer to an unblemished, unwrinkled surface, such as that of a bloated tick, rather than to fatness or general bodily health. The source of the Suda's other sentence is unknown.
Eustathius, on the other hand, follows Strabo 6.1.12.31f. and argues (Commentary on Dionysius Periegetes 369.18-32, cf. Commentary on the Odyssey 2.147.23-30) that the phrase refers to the proverbial athletic training and physical health of the people of Croton (sc. under the Pythagorean regime). He regards the other interpretation as a mere jest of comedians, playing on words. It may be fair to say that the two meanings were never far from the mind of someone using the proverb. Eustathius too ignores Herodian's distinction, although it would have supported his argument.
[1] The verb dei= is here supplied from the entry's source in Photius (as emended: see above).