Books have been written about the "Noble Savage" aesthetic that was so popular in those days. It comes across as patronizing but not overtly hostile, and the artists of that era most likely felt they were creating sympathetic portrayals of their subjects. But you can't really consider this kind of thing in isolation; it was a product -- not a critique -- of the political and economic climate at the time, which was anything but sympathetic toward the Indian population. The key idea behind "Noble Savage" art was that the Indians were a proud, honorable people, sadly destined to "make way" for the White Man, in the name of Progress. Which is a fancy way of saying, "We're fascinated by you, we even admire you in some respects, but we're still taking your land."
The city parks page for Washington Park gives a bit of background on the piece:
Coming of the White Man was given to the city by the heirs of David P. Thompson, an early Portland mayor and donor of the elk statue on Main between the Plaza Blocks. Completed in 1904, this bronze statue, sculpted by Hermon Atkins MacNeil and cast by Bureau Brothers Foundry in Los Angeles, features two Native Americans standing on a block of rough-hewn native stone. Facing eastward, they look down upon the route that ox teams trudged bringing settlers to this part of the country. The older of the two is said to represent Chief Multnomah of the Multnomah people. At some point, the oak branch held by the younger figure was broken off.
Chicago's Field Museum has a circa-1910 vintage photo of the sculpture in their Flickr stream. It looks about the same as it does now; I pass it along because the caption mentions it was taken by the Huron H. Smith expedition to Oregon, which came here to collect botanical samples and take portraits of trees, as if Portland was a barely settled frontier town. It amuses me that they were still using the word "expedition" in 1910, as if they were visiting Antarctica, or a remote spot in the Amazon rainforest, or the "unexplored" Pacific Northwest of a century earlier. If you can arrive by train, and can then wander around town taking photos of contemporary art and such, you should probably be using the word "expedition" at least semi-ironically. Which is more or less what I do here on this humble blog.