The headword phrase is presumably extracted from the quotation given.
[1] For a (fortuitous) near-reversal of this headword phrase and gloss, see Aeschines 2.40 (web address 1) with scholion. Aeschines is accusing his political rival Demosthenes of 'unexpectedly' disclosing to him the meaning of three vulgar expressions (kappa 1410, pi 88, pi 887); Maxwell-Stuart, pp. 7-12) and the scholiast glosses the adverb as 'contrary to his own nature'.
[2] Aelian fr. 313 Hercher (310 Domingo-Forasté), contextless. [In her critical apparatus, Adler notes that ms. M and the corrected edition of ms. F read peri\: imputable to their own nature.]