I am using Pages 6.2 on macOS 10.12.5. Within Pages settings, Auto-Correction > Correct Spelling Automatically is disabled. I unchecked the Edit > Spelling and Grammar > Check Spelling While Typing menu item. I unchecked the Edit > Substitutions > Text Replacement menu item. Within System Preferences, Keyboard > Text > Correct spelling automatically is disabled. Within Pages, if I select my document's table, open the Format pane on the right, and select Table, I don't see any options regarding spelling correction or autocompletion.
My Pages document consists of a table, with column A consisting of a list of languages, and columns B-K containing translations of the cardinal numbers zero through nine in that row's language. So this is a multi-lingual document, and any suggestions for spelling correction or text substitution are likely to be wrong, and are unwanted.
Let's say I go to row 8 (8A contains "Czech"), column B, and type zer, assuming that this is the exact text that I want to appear there. I see a popup below this cell containing two values: "zéro", "zero". I want neither of these. What key do I press to dismiss the popup? If I press Esc, sometimes the cell is cleared and sometimes my entered text remains as intended. If I press tab, instead of advancing to the next cell, a selection row appears within the unwanted completion suggestions popup. I can click on the next cell (8C), however I should be able to complete my entry without using the mouse. After all, I disabled "Correct spelling automatically" in both applicable locations.
I've found that I can press the right arrow key, then tab, to advance to the next cell without any autocompletion. However, this seems like more work than necessary given that I've disabled all autocomplete options that I can find. Since I am editing over 550 cells in this document alone, I want to do this as efficiently as possible.
I also did a quick test of Numbers 4.2, and I experience the same problem with unwanted completion suggestions appearing in a popup below the cell that must be interacted with before the Tab key will advance to the next cell.