The million sales mark was from one single report by Kuo. Kuo himself previously said they were limited to ~900K display units which is ~450K devices and other analysts have said the same.
There is no other source saying 1M was the target that I know of that doesn’t trace back to Kuo. If they are at ~500K units then they’ve exceeded the initial sales target that Kuo himself laid out.
For your second point about a follow up, you’re comparing product announcement to product launches. The product itself only launched 10months ago. You’re expecting a second iteration within 10 months, of an entirely new product class for them ? Meanwhile other more popular Apple products often go longer between releases. Even Meta are around two years between products within a device class.
Your last point of comparing to a meta quest is misplaced too. They’re different classes of the same device category. There’s no way Apple are expecting to compete with a device a tenth of its price for total sales.