Or HaChaim on Exodus 14:22/אור החיים על שמות י״ד:כ״ב

1 בתוך הים ביבשה, in the midst of the sea on dry land. The words "in the midst of the sea" mean in the inner part of (what had formerly been) the sea; the word ביבשה means that the sea bed was not muddy but completely dry.

2והמים להם חומה, and the waters formed a wall for them, etc. This means that parts of the waters had not been blown aside by the wind. The words: "on their right and on their left" mean that those waters did not form an actual wall but merely that they surrounded the Israelites on either side.