Of course not. The HMS Beagle only spent 5 week in the area. Neither Darwin nor anybody else claimed he observed evolution!
The Galápagos Islands consist of 22 main islands spread over 28,000 square miles.
Charles Darwin found roughly 13 different types of finch populating it, and he went about collecting the new (to him) specimens for later classification. But after his return to England, ornithologist John Gould told him that the finches were not, as Darwin had supposed, members of several widely different families, but all belonged to one family now known as the Geospizinae.
That's when it clicked that the birds became isolated on their individual islands and had adapted to their local environment.
It is the classic example of "Adaptive Radiation", a process of evolution in which variations of a single species fill different niches and eventually become new species.
A common misconception is to equate the theory evolution with natural selection. Long before Darwin, folks were observing evolution. He just explained the mechanism, natural selection.