If your entire career relies on your knowing stuff, then it makes sense that you would learn some magic at some point, since magic is just knowledge. Skilled bards should have some magical ability.
Since you aren't spending your entire life in a tower with a bunch of scrolls, then it makes sense that you would pick up the basics of how to defend yourself with weapons. Bards should not be as bad at fighting as wizards are.
Since you aren't a professional warrior, and you don't have enough magic to really rely on it, then it makes sense that you would learn how to hide and avoid fights.
As a whole, the bard class makes plenty of sense, as it was presented in the AD&D 2E PHB - it's the class which learned a little bit of everything, and incidentally could play an instrument although that pretty much never mattered.
What the class has since devolved into is just a jumbled mess of pointless high-magic mumbo-jumbo that doesn't make any sense outside of the Forgotten Realms.