In this poem, the speaker is evasive about their exact actions. At the outset, the only verb that indicates any action on their part is "wandered." This could literally mean that the speaker was walking aimlessly at that moment, or it could refer more generally to their activities and attitudes over an unspecified period of time. The marked change in Line 3, "all at once I saw" is amplified in Line 11, when the speaker repeats the verb "saw." No other action is offered on the speaker's part. Rather, the flowers are said to be dancing or looking like they are dancing, and the waves dance as well. Again in Line 17, the poet says "I gazed—and gazed—but little thought...": the primary activity is looking, and the secondary is thinking but only a little.
Overall, the impression of passive observer is emphasized. Even when the speaker acknowledges a change in mood, they do so in the third person: "A poet could not be but gay...." The related shift is from "lonely" to feeling accompanied: "in such a jocund company."