I can't get a hold of a raw version so i can't be certain that there's not some evidence in there that this kanji should be read as 'tenkuni', but in any other case this would be read with the on-yomi, making it 'tengoku'--an actual word in japanese dictionaries. Caterpillar does a great job with the scans for Maruo so if that was their call i trust it, but I don't yet understand.