Morrison says that Mr. Elliot phrased that wish very carefully, so as to cover himself. If Anne had not responded, if her face had not glowed with joy and acceptance, he could have backtracked easily to simply repeating that he had always liked the sound of her name.

To me, it is too clearly a proposal, and any retraction would have been awkward and unbelievable.

However, more to the point is Anne's apparent refusal to understand Mr. Elliot: assuming that she believed what she said when Mrs. Smith accused her of forming a future with Mr. Elliot. Either she did not gather what he had said (in which case, why did she start avoiding Mr. Elliot from that moment on?); or she heard him and thought that her throwing cold water on their acquaintance would keep him from repeating his suggestion.