That Julius Caesar definitely never wore pants? I have no source.
That Romans at the time did not, for the most part, wear pants? It's a DDG search away:
"Even when foreign garments – such as full-length trousers – proved more practical than standard issue, soldiers and commanders who used them were viewed with disdain and alarm by their more conservative compatriots, for undermining Rome's military virtus by "going native". ... Trousers – considered barbarous garments worn by Germans and Persians – achieved only limited popularity in the latter days of the empire, and were regarded by conservatives as a sign of cultural decay." - https://en.wikipedia.org/wiki/Clothing_in_ancient_Rome
"But in Imperial Rome, obviously, things were a little different—no man of honor would think of wearing what was considered the garb of a savage barbarian." https://www.atlasobscura.com/articles/trousers-pants-roman-h...
"For the Romans, to encircle the legs and thighs with fasciae, or bands, was understood, in the time of Pompey and Horace, to be a proof of ill health and effeminacy.[2] Roman men typically wore tunics, which were one-piece outfits terminating at or above the knee." - https://en.wikipedia.org/wiki/Braccae
"Leg coverings were seen as crude items, something that was worn by the barbarians who lived beyond the borders of Roman civilization or as the leg protection of the very poor or old. Long pants, like long sleeves were seen as effeminate. ... In Caesar's day braccae were considered effeminate and barbarian-wear — something to avoided by civilized Roman men." - https://romanobritain.org/8-military/mil_soldiers_braccae_.p...
Digging more, I found this from "Roman Influences on the Victory Reliefs of Shapur I of Persia", Marjorie C. Mackintosh, California Studies in Classical Antiquity , 1973, Vol. 6 (1973), pp. 181-203, https://www.jstor.org/stable/pdf/25010653.pdf
> On the Column of Marcus Aurelius, the emperor addresses his men who, like himself, are clad in tunica, sagum and bracae (Hamberg [supra n. 22] 143, pl. 26, scene LXXXIII). See also Brilliant, Severus, 155, n. 23. That the Romans on the other reliefs do not wear the same may have been due to an oversight or to the fact that the Romans considered trousers as a basically barbarian garment (E. Sander, Die Kleidung des romischen Soldaten," Historia 12 [1963] 152) and may have preferred not to be depicted thus in a "barbarian" monument. Since the Romans probably helped in the design of the monuments, their preference might have had some force. Roman monuments show emperors and officers in field situations both with and without bracae.
So, maybe Julius Caesar did sometimes wear pants? You'll need to ask a Romanologist.
Still, there's going to be plenty of Roman flute players who never wore pants.