Did every booster of Unglued contain basic land?
Every pack of Unglued should contain a basic land, barring any collation issues.

After fourth edition all large sets used a separate sheet for basic lands, but small sets still had their lands printed on the common sheet (why use extra sheets when you have 110-121 slots to fill?).

While the sheet distribution for Unglued isn't known, at 94 cards it definitely falls into the small set category, and most likely only had two print sheets.