The Analect 2.2 quotes from the Book of Odes, and Arthur Waley claims there is a difference between how Confucius there reads the character 思 (sī, think) and how it was used in the Ode. Waley claims that in the Ode "ssu does not mean 'thoughts', but is an exclamation, 'oh', 'ah', or the like." I looked at the various old dictionary definitions, and textual examples on the Chinese Text Project https://ctext.org/ and I did not find any evidence there that 思 was ever used the way Waley says. It always seems to mean "thought(s)" or "think." Other searches got me nothing relevant.
Is there evidence supporting Waley's claim?