When you add a new section using NWE, spellchecking is not enabled by default for the title input (at least in Firefox), because <input> fields aren't spellchecked by default.
Setting spellcheck="true" (https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/spellcheck) enables spellchecking for the title as well, and I don't see any reason not to do so.