In any case, explaining its meaning does not fall within the interpretation that Allah has reserved to Himself, whether or not such explanation is called interpretation. As for their argument based on the disconnected letters, there are several answers.

First, these do not constitute connected discourse and therefore do not fall under the designation of verses. Most people—the people of Mecca, Medina, and Basra—do not count them as a verse, whereas the Kufans do. In any case, they are names of letters, pronounced without grammatical inflection, just as one pronounces alif, bā, tā, or the names of numbers: one, two, three. Meaning becomes clear when they are joined and combined. Even supposing that these letters have no intelligible meaning, it does not follow that connected, ordered discourse forming a nominal or verbal sentence has no intelligible meaning. On that supposition, however, these letters would have been revealed on some basis other than that of addressing people.

The second answer is that the early generations did discuss their meanings. Their statements on this subject are numerous and well known, transmitted from Ibn ʿAbbās and others. To elaborate here: sometimes they say that each letter points to one of the names of Allah Most High.