The word: حُسبانا - (husbana) in Al-Kahf 18:40 ⧉ has been explained by Qatadah as 'punishment' in an absolute sense, by Sayyidna Ibn ` Abbas ؓ as 'fire' and by some as 'stoning.' As for what appears after that in the Qur'an: أُحِيطَ بِثَمَرِهِ (And its produce was struck by destruction from all sides — Al-Kahf 18:42 ⧉), it obviously means that some major calamity hit his gardens, wealth and things of luxury reducing everything to ruins. The Qur'an does not mention any particular calamity explicitly. It appears that, some fire came down from the skies and burnt the whole thing - as it appears in the Tafsir of 'husban' by Sayyidna Ibn 'Abbas ؓ who has explained it as 'fire.' And Allah knows best.